SEASONING OF WOOD

A TREATISE ON THE NATURAL AND ARTIFICIAL
PROCESSES EMPLOYED IN THE PREPARATION
OF LUMBER FOR MANUFACTURE,
WITH DETAILED EXPLANATIONS OF ITS
USES, CHARACTERISTICS AND PROPERTIES

ILLUSTRATIONS

BY
JOSEPH B. WAGNER
AUTHOR OF “COOPERAGE”

NEW YORK
D. VAN NOSTRAND COMPANY
25 PARK PLACE
1917

COPYRIGHT, 1917, BY
D. VAN NOSTRAND COMPANY

THE·PLIMPTON·PRESS
NORWOOD·MASS·U·S·A

PREFACE[v]

The seasoning and kiln-drying of wood is such an important
process in the manufacture of woods that a need
for fuller information regarding it, based upon scientific
study of the behavior of various species at different mechanical
temperatures, and under different drying processes
is keenly felt. Everyone connected with the
woodworking industry, or its use in manufactured products,
is well aware of the difficulties encountered in
properly seasoning or removing the moisture content
without injury to the timber, and of its susceptibility to
atmospheric conditions after it has been thoroughly
seasoned. There is perhaps no material or substance that
gives up its moisture with more resistance than wood does.
It vigorously defies the efforts of human ingenuity to take
away from it, without injury or destruction, that with
which nature has so generously supplied it.

In the past but little has been known of this matter
further than the fact that wood contained moisture which
had to be removed before the wood could be made use of
for commercial purposes. Within recent years, however,
considerable interest has been awakened among wood-users
in the operation of kiln-drying. The losses occasioned
in air-drying and improper kiln-drying, and the
necessity for getting the material dry as quickly as possible
after it has come from the saw, in order to prepare
it for manufacturing purposes, are bringing about a realization
of the importance of a technical knowledge of
the subject.

Since this particular subject has never before been represented
by any technical work, and appears to have been
neglected, it is hoped that the trade will appreciate the endeavor
in bringing this book before them, as well as the
difficulties encountered in compiling it, as it is the first of[vi]
its kind in existence. The author trusts that his efforts
will present some information that may be applied with
advantage, or serve at least as a matter of consideration
or investigation.

In every case the aim has been to give the facts, and
wherever a machine or appliance has been illustrated or
commented upon, or the name of the maker has been
mentioned, it has not been with the intention either of
recommending or disparaging his or their work, but has
been made use of merely to illustrate the text.

The preparation of the following pages has been a work
of pleasure to the author. If they prove beneficial and
of service to his fellow-workmen he will have been amply
repaid.

THE AUTHOR.

September, 1917

CONTENTS[vii]

LIST OF ILLUSTRATIONS[xi]

SEASONING OF WOOD[1]

SECTION I

TIMBER

Characteristics and Properties

Timber was probably one of the earliest, if not the
earliest, of materials used by man for constructional purposes.
With it he built for himself a shelter from the
elements; it provided him with fuel and oft-times food,
and the tree cut down and let across a stream formed the
first bridge. From it, too, he made his “dug-out” to
travel along and across the rivers of the district in which
he dwelt; so on down through the ages, for shipbuilding
and constructive purposes, timber has continued to our
own time to be one of the most largely used of nature’s
products.

Although wood has been in use so long and so universally,
there still exists a remarkable lack of knowledge regarding
its nature, not only among ordinary workmen, but
among those who might be expected to know its properties.
Consequently it is often used in a faulty and wasteful
manner. Experience has been almost the only teacher,
and theories—sometimes right, sometimes wrong—rather
than well substantiated facts, lead the workman.

One reason for this imperfect knowledge lies in the fact
that wood is not a homogeneous material, but a complicated
structure, and so variable, that one piece will behave
very differently from another, although cut from the same
tree. Not only does the wood of one species differ from
that of another, but the butt cut differs from that of the
top log, the heartwood from the sapwood; the wood of
quickly-grown sapling of the abandoned field, from[2]
that of the slowly-grown, old monarch of the forest. Even
the manner in which the tree was cut and kept influences
its behavior and quality. It is therefore extremely difficult
to study the material for the purpose of establishing
general laws.

The experienced woodsman will look for straight-grained,
long-fibred woods, with the absence of disturbing
resinous and coloring matter, knots, etc., and will
quickly distinguish the more porous red or black oaks from
the less porous white species, Quercus alba. That the
inspection should have regard to defects and unhealthy
conditions (often indicated by color) goes without saying,
and such inspection is usually practised. That knots,
even the smallest, are defects, which for some uses condemn
the material entirely, need hardly be mentioned.
But that “season-checks,” even those that have closed
by subsequent shrinkage, remain elements of weakness
is not so readily appreciated; yet there cannot be any
doubt of this, since these, the intimate connections of
the wood fibres, when once interrupted are never reestablished.

Careful woods-foremen and manufacturers, therefore,
are concerned as to the manner in which their timber is
treated after the felling, for, according to the more or less
careful seasoning of it, the season checks—not altogether
avoidable—are more or less abundant.

There is no country where wood is more lavishly used
or criminally neglected than in the United States, and
none in which nature has more bountifully provided for
all reasonable requirements.

In the absence of proper efforts to secure reproduction,
the most valuable kinds are rapidly being decimated, and
the necessity of a more rational and careful use of what
remains is clearly apparent. By greater care in selection,
however, not only will the duration of the supply be extended,
but more satisfactory results will accrue from its
practice.

There are few more extensive and wide-reaching subjects
on which to treat than timber, which in this book
refers to dead timber—the timber of commerce—as[3]
distinct from the living tree. Such a great number of
different kinds of wood are now being brought from various
parts of the world, so many new kinds are continually
being added, and the subject is more difficult to explain
because timber of practically the same character which
comes from different localities goes under different names,
that if one were always to adhere to the botanical name
there would be less confusion, although even botanists
differ in some cases as to names. Except in the cases of
the older and better known timbers, one rarely takes up
two books dealing with timber and finds the botanical
names the same; moreover, trees of the same species may
produce a much poorer quality of timber when obtained
from different localities in the same country, so that botanical
knowledge will not always allow us to dispense with
other tests.

The structure of wood affords the only reliable means
of distinguishing the different kinds. Color, weight, smell,
and other appearances, which are often direct or indirect
results of structure, may be helpful in this distinction,
but cannot be relied upon entirely. Furthermore, structure
underlies nearly all the technical properties of this
important product, and furnishes an explanation why one
piece differs in these properties from another. Structure
explains why oak is heavier, stronger, and tougher than
pine; why it is harder to saw and plane, and why it is so
much more difficult to season without injury. From its
less porous structure alone it is evident that a piece of
young and thrifty oak is stronger than the porous wood
of an old or stunted tree, or that a Georgia or long-leaf
pine excels white pine in weight and strength.

Keeping especially in mind the arrangement and direction
of the fibres of wood, it is clear at once why knots and
“cross-grain” interfere with the strength of timber. It
is due to the structural peculiarities that “honeycombing”
occurs in rapid seasoning, that checks or cracks extend
radially and follow pith rays, that tangent or “bastard”
cut stock shrinks and warps more than that which is
quarter-sawn. These same peculiarities enable oak to
take a better finish than basswood or coarse-grained pine.[4]

Structure of Wood

The softwoods are made up chiefly of tracheids, or
vertical cells closed at the ends, and of the relatively short
parenchyma cells of the medullary rays which extend
radially from the heart of the tree. The course of the
tracheids and the rays are at right angles to each other.
Although the tracheids have their permeable portions or
pits in their walls, liquids cannot pass through them with
the greatest ease. The softwoods do not contain “pores”
or vessels and are therefore called “non-porous” woods.

The hardwoods are not so simple in structure as softwoods.
They contain not only rays, and in many cases
tracheids, but also thick-walled cells called fibres and wood
parenchyma for the storage of such foods as starches and
sugars. The principal structural features of the hardwoods
are the pores or vessels. These are long tubes, the
segments of which are made up of cells which have lost
their end walls and joined end to end, forming continuous
“pipe lines” from the roots to the leaves in the tree. Since
they possess pores or vessels, the hardwoods are called
“porous” woods.

Red oak is an excellent example of a porous wood. In
white oak the vessels of the heartwood especially are
closed, very generally by ingrowths called tyloses. This
probably explains why red oak dries more easily and
rapidly than white oak.

The red and black gums are perhaps the simplest of the
hardwoods in structure. They are termed “diffuse porous”
woods because of the numerous scattered pores
they contain. They have only vessels, wood fibres, and
a few parenchyma cells. The medullary rays, although
present, are scarcely visible in most instances. The
vessels are in many cases open, and might be expected to
offer relatively little resistance to drying.

Properties of Wood

Certain general properties of wood may be discussed
briefly. We know that wood substance has the property
of taking in moisture from the air until some balance is[5]
reached between the humidity of the air and the moisture
in the wood. This moisture which goes into the cell walls
hygroscopic moisture, and the property which the wood
substance has of taking on hygroscopic moisture is termed
hygroscopicity. Usually wood contains not only hygroscopic
moisture but also more or less free water in the
cell cavities. Especially is this true of sapwood. The
free water usually dries out quite rapidly with little or no
shrinkage or other physical change.

In certain woods—for example, Eucalyptus globulus and
possibly some oaks—shrinkage begins almost at once, thus
introducing a factor at the very start of the seasoning process
which makes these woods very refractory.

The cell walls of some species, including the two already
mentioned, such as Western red cedar and redwood, become
soft and plastic when hot and moist. If the fibres
are hot enough and very wet, they are not strong enough
to withstand the resulting force of the atmospheric pressure
and the tensile force exerted by the departing free
water, and the result is that the cells actually collapse.

In general, however, the hygroscopic moisture necessary
to saturate the cell walls is termed the “fibre saturation
point.” This amount has been found to be from
25 to 30 per cent of the dry wood weight. Unlike Eucalyptus
globulus and certain oaks, the gums do not begin
to shrink until the moisture content has been reduced to
about 30 per cent of the dry wood weight. These woods
are not subject to collapse, although their fibres become
very plastic while hot and moist.

Upon the peculiar properties of each wood depends the
difficulty or ease of the seasoning process.

Classes of Trees

The timber of the United States is furnished by three
well-defined classes of trees: (1) The needle-leaved, naked-seeded
conifers, such as pine, cedar, etc., (2) the broad-leaved
trees such as oak poplar, etc., and (3) to an
inferior extent by the (one-seed leaf) palms, yuccas,
and their allies, which are confined to the most southern
parts of the country.[6]

Broad-leaved trees are also known as deciduous trees,
although, especially in warm countries, many of them are
evergreen, while the needle-leaved trees (conifers) are
commonly termed “evergreens,” although the larch, bald
cypress, and others shed their leaves every fall, and even
the names “broad-leaved” and “coniferous,” though perhaps
the most satisfactory, are not at all exact, for the
conifer “ginkgo” has broad leaves and bears no cones.

Among the woodsmen, the woods of broad-leaved trees
are known as “hardwoods,” though poplar is as soft as
pine, and the “coniferous woods” are known as “softwoods,”
notwithstanding the fact that yew ranks high in
hardness even when compared with “hardwoods.”

Both in the number of different kinds of trees or species
and still more in the importance of their product, the conifers
and broad-leaved trees far excel the palms and their
relatives.

In the manner of their growth both the conifers and
broad-leaved trees behave alike, adding each year a new
layer of wood, which covers the old wood in all parts of
the stem and limbs. Thus the trunk continues to grow
in thickness throughout the life of the tree by additions
(annual rings), which in temperate climates are, barring
accidents, accurate records of the tree. With the palms
and their relatives the stem remains generally of the same
diameter, the tree of a hundred years old being as thick
as it was at ten years, the growth of these being only at
the top. Even where a peripheral increase takes place,
as in the yuccas, the wood is not laid on in well-defined
layers for the structure remains irregular throughout.
Though alike in the manner of their growth, and therefore
similar in their general make-up, conifers and broad-leaved
trees differ markedly in the details of their structure and
the character of their wood.

The wood of all conifers is very simple in its structure,
the fibres composing the main part of the wood all being
alike and their arrangement regular. The wood of the
broad-leaved trees is complex in structure; it is made up
of different kinds of cells and fibres and lacks the regularity
of arrangement so noticeable in the conifers. This[7]
difference is so great that in a study of wood structure it
is best to consider the two kinds separately.

In this country the great variety of woods, and especially
of useful woods, often makes the mere distinction of the
kind or species of tree most difficult. Thus there are at
least eight pines of the thirty-five native ones in the market,
some of which so closely resemble each other in their
minute structure that one can hardly tell them apart, and
yet they differ in quality and are often mixed or confounded
in the trade. Of the thirty-six oaks, of which
probably not less than six or eight are marketed, we can
readily recognize by means of their minute anatomy at
least two tribes—the white and black oaks. The same
is true of the eleven kinds of hickory, the six kinds of ash,
etc., etc.

The list of names of all trees indigenous to the United
States, as enumerated by the United States Forest Service,
is 495 in number, the designation of “tree” being applied
to all woody plants which produce naturally in their
native habitat one main, erect stem, bearing a definite
crown, no matter what size they attain.

Timber is produced only by the Spermatophyta, or
seed-bearing plants, which are subdivided into the Gymnosperms
(conifers), and Angiosperms (broad-leaved).
The conifer or cone-bearing tree, to which belong the pines,
larches, and firs, is one of the three natural orders of Gymnosperms.
These are generally classed as “softwoods,”
and are more extensively scattered and more generally
used than any other class of timber, and are simple and
regular in structure. The so-called “hardwoods” are
“Dicotyledons” or broad-leaved trees, a subdivision of
the Angiosperms. They are generally of slower growth,
and produce harder timber than the conifers, but not
necessarily so. Basswood, poplar, sycamore, and some
of the gums, though classed with the hardwoods, are not
nearly as hard as some of the pines.

SECTION II[8]

CONIFEROUS TREES

WOOD OF THE CONIFEROUS TREES

Examining a smooth cross-section or end face of a well-grown
log of Georgia pine, we distinguish an envelope of
reddish, scaly bark, a small, whitish pith at the center,
and between these the wood in a great number of concentric
rings.

Bark and Pith

The bark of a pine stem is thickest and roughest near
the base, decreases rapidly in thickness from one to one-half
inches at the stump to one-tenth inch near the top
of the tree, and forms in general about ten to fifteen per
cent of the entire trunk. The pith is quite thick, usually
one-eighth to one-fifth inch in southern species, though
much less so in white pine, and is very thin, one-fifteenth
to one twenty-fifth inch in cypress, cedar, and larch.

In woods with a thick pith, the pith is finest at the
stump, grows rapidly thicker toward the top, and becomes
thinner again in the crown and limbs, the first one
to five rings adjoining it behaving similarly.

What is called the pith was once the seedling tree, and
in many of the pines and firs, especially after they have
been seasoning for a good while, this is distinctly noticeable
in the center of the log, and detaches itself from the
surrounding wood.

Sap and Heartwood

Wood is composed of duramen or heartwood, and alburnum
or sapwood, and when dry consists approximately
of 49 per cent by weight of carbon, 6 per cent of hydrogen,
44 per cent of oxygen, and 1 per cent of ash, which is fairly
uniform for all species. The sapwood is the external and[9]
youngest portion of the tree, and often constitutes a very
considerable proportion of it. It lies next the bark, and
after a course of years, sometimes many, as in the case of
oaks, sometimes few, as in the case of firs, it becomes
hardened and ultimately forms the duramen or heartwood.
Sapwood is generally of a white or light color, almost invariably
lighter in color than the heartwood, and is very
conspicuous in the darker-colored woods, as for instance
the yellow sapwood of mahogany and similiar colored
woods, and the reddish brown heartwood; or the yellow
sapwood of Lignum-vitae and the dark green heartwood.
Sapwood forms a much larger proportion of some trees
than others, but being on the outer circumference it always
forms a large proportion of the timber, and even in sound,
hard pine will be from 40 per cent to 60 per cent of the
tree and in some cases much more. It is really imperfect
wood, while the duramen or heartwood is the perfect wood;
the heartwood of the mature tree was the sapwood of its
earlier years. Young trees when cut down are almost
all sapwood, and practically useless as good, sound timber;
it is, however, through the sapwood that the life-giving
juices which sustain the tree arise from the soil, and if the
sapwood be cut through, as is done when “girdling,” the
tree quickly dies, as it can derive no further nourishment
from the soil. Although absolutely necessary to the growing
tree, sapwood is often objectionable to the user, as it
is the first part to decay. In this sapwood many cells are
active, store up starch, and otherwise assist in the life
processes of the tree, although only the last or outer layer
of cells forms the growing part, and the true life of the tree.

The duramen or heartwood is the inner, darker part of
the log. In the heartwood all the cells are lifeless cases,
and serve only the mechanical function of keeping the
tree from breaking under its own great weight or from
being laid low by the winds. The darker color of the
heartwood is due to infiltration of chemical substances
into the cell walls, but the cavities of the cells in pine are
not filled up, as is sometimes believed, nor do their walls
grow thicker, nor are the walls any more liquified than in
the sapwood.[10]

Sapwood varies in width and in the number of rings
which it contains even in different parts of the same tree.
The same year’s growth which is sapwood in one part of
a disk may be heartwood in another. Sapwood is widest
in the main part of the stem and often varies within considerable
limits and without apparent regularity. Generally,
it becomes narrower toward the top and in the
limbs, its width varying with the diameter, and being
the least in a given disk on the side which has the shortest
radius. Sapwood of old and stunted pines is composed
of more rings than that of young and thrifty specimens.
Thus in a pine two hundred and fifty years old a layer of
wood or an annual ring does not change from sapwood to
heartwood until seventy or eighty years after it is formed,
while in a tree one hundred years old or less it remains
sapwood only from thirty to sixty years.

The width of the sapwood varies considerably for different
kinds of pine. It is small for long-leaf and white
pine and great for loblolly and Norway pines. Occupying
the peripheral part of the trunk, the proportion which
it forms of the entire mass of the stem is always great.
Thus even in old long-leaf pines, the sapwood forms 40
per cent of the merchantable log, while in the loblolly
and in all young trees the sapwood forms the bulk of the
wood.

The Annual or Yearly Rings

The concentric annual or yearly rings which appear on
the end face of a log are cross-sections of so many thin
layers of wood. Each such layer forms an envelope around
its inner neighbor, and is in turn covered by the adjoining
layer without, so that the whole stem is built up of
a series of thin, hollow cylinders, or rather cones.

A new layer of wood is formed each season, covering
the entire stem, as well as all the living branches. The
thickness of this layer or the width of the yearly ring
varies greatly in different trees, and also in different parts
of the same tree.

In a normally-grown, thrifty pine log the rings are widest
near the pith, growing more and more narrow toward[11]
the bark. Thus the central twenty rings in a disk of an
old long-leaf pine may each be one-eighth to one-sixth
inch wide, while the twenty rings next to the bark may
average only one-thirtieth inch.

In our forest trees, rings of one-half inch in width occur
only near the center in disks of very thrifty trees, of both
conifers and hardwoods. One-twelfth inch represents good,
thrifty growth, and the minimum width of one two hundred
inch is often seen in stunted spruce and pine. The
average width of rings in well-grown, old white pine will
vary from one-twelfth to one-eighteenth inch, while in the
slower growing long-leaf pine it may be one twenty-fifth
to one-thirtieth of an inch. The same layer of wood
is widest near the stump in very thrifty young trees,
especially if grown in the open park; but in old forest
trees the same year’s growth is wider at the upper part
of the tree, being narrowest near the stump, and often
also near the very tip of the stem. Generally the rings
are widest near the center, growing narrower toward the
bark.

In logs from stunted trees the order is often reversed,
the interior rings being thin and the outer rings widest.
Frequently, too, zones or bands of very narrow rings,
representing unfavorable periods of growth, disturb the
general regularity.

Few trees, even among pines, furnish a log with truly
circular cross-section. Usually it is an oval, and at the
stump commonly quite an irregular figure. Moreover,
even in very regular or circular disks the pith is rarely in
the center, and frequently one radius is conspicuously
longer than its opposite, the width of some rings, if not
all, being greater on one side than on the other. This is
nearly always so in the limbs, the lower radius exceeding
the upper. In extreme cases, especially in the limbs, a
ring is frequently conspicuous on one side, and almost
or entirely lost to view on the other. Where the rings
are extremely narrow, the dark portion of the ring is often
wanting, the color being quite uniform and light. The
greater regularity or irregularity of the annual rings has
much to do with the technical qualities of the timber.[12]

Spring- and Summer-Wood

Examining the rings more closely, it is noticed that
each ring is made up of an inner, softer, light-colored and
an outer, or peripheral, firmer and darker-colored portion.
Being formed in the forepart of the season, the inner,
light-colored part is termed spring-wood, the outer, darker-portioned
being the summer-wood of the ring. Since the
latter is very heavy and firm it determines to a very large
extent the weight and strength of the wood, and as its
darker color influences the shade of color of the entire
piece of wood, this color effect becomes a valuable aid in
distinguishing heavy and strong from light and soft pine
wood.

In most hard pines, like the long-leaf, the dark summer-wood
appears as a distinct band, so that the yearly ring
is composed of two sharply defined bands—an inner,
the spring-wood, and an outer, the summer-wood. But
in some cases, even in hard pines, and normally in the
woods of white pines, the spring-wood passes gradually
into the darker summer-wood, so that a darkly defined
line occurs only where the spring-wood of one ring abuts
against the summer-wood of its neighbor. It is this clearly
defined line which enables the eye to distinguish even the
very narrow lines in old pines and spruces.

In some cases, especially in the trunks of Southern pines,
and normally on the lower side of pine limbs, there occur
dark bands of wood in the spring-wood portion of the ring,
giving rise to false rings, which mislead in a superficial
counting of rings. In the disks cut from limbs these
dark bands often occupy the greater part of the ring, and
appear as “lunes,” or sickle-shaped figures. The wood of
these dark bands is similar to that of the true summer-wood.
The cells have thick walls, but usually the compressed
or flattened form. Normally, the summer-wood
forms a greater proportion of the rings in the part of the
tree formed during the period of thriftiest growth. In
an old tree this proportion is very small in the first two
to five rings about the pith, and also in the part next to
the bark, the intermediate part showing a greater proportion[13]
of summer-wood. It is also greatest in a disk
taken from near the stump, and decreases upward in the
stem, thus fully accounting for the difference in weight
and firmness of the wood of these different parts.

In the long-leaf pine the summer-wood often forms
scarcely ten per cent of the wood in the central five rings;
forty to fifty per cent of the next one hundred rings, about
thirty per cent of the next fifty, and only about twenty
per cent in the fifty
rings next to the
bark. It averages
forty-five per cent of
the wood of the
stump and only
twenty-four per cent
of that of the top.

Sawing the log into
boards, the yearly
rings are represented
on the board faces
of the middle board
(radial sections) by
narrow parallel strips
(see Fig. 1), an inner,
lighter stripe
and its outer, darker
neighbor always corresponding
to one
annual ring.

On the faces of the
boards nearest the slab (tangential or bastard boards) the
several years’ growth should also appear as parallel, but
much broader stripes. This they do if the log is short
and very perfect. Usually a variety of pleasing patterns
is displayed on the boards, depending on the position of
the saw cut and on the regularity of growth of the log
(see Fig. 1). Where the cut passes through a prominence
(bump or crook) of the log, irregular, concentric circlets
and ovals are produced, and on almost all tangent boards
arrow or V-shaped forms occur.[14]

Anatomical Structure

Holding a well-smoothed disk or cross-section one-eighth
inch thick toward the light, it is readily seen that
pine wood is a very porous structure. If viewed with a
strong magnifier, the little tubes, especially in the spring-wood
of the rings, are easily distinguished, and their arrangement
in regular, straight, radial rows is apparent.

Scattered through the summer-wood portion of the
rings, numerous irregular grayish dots (the resin ducts)
disturb the uniformity
and regularity of
the structure. Magnified
one hundred
times, a piece of
spruce, which is similar
to pine, presents
a picture like that
shown in Fig. 2.
Only short pieces of
the tubes or cells of
which the wood is
composed are represented
in the picture.
The total length of
these fibres is from
one-twentieth to one-fifth
inch, being the
smallest near the
pith, and is fifty to
one hundred times
as great as their
width (see Fig. 3).
They are tapered and closed at their ends, polygonal or
rounded and thin-walled, with large cavity, lumen or internal
space in the spring-wood, and thick-walled and
flattened radially, with the internal space or lumen much
reduced in the summer-wood (see right-hand portion
of Fig. 2). This flattening, together with the thicker walls
of the cells, which reduces the lumen, causes the greater[15]
firmness and darker color of the summer-wood. There
is more material in the same volume. As shown in the
figure, the tubes, cells or “tracheids” are decorated on
their walls by circlet-like structures, the “bordered pits,”
sections of which are seen more magnified as a, b, and c,
Fig. 2. These pits are in the nature of pores, covered
by very thin membranes, and serve as waterways
between the cells or tracheids. The dark
lines on the side of the smaller piece (1, Fig. 2)
appear when magnified (in 2, Fig. 2) as tiers
of eight to ten rows of cells, which run radially
(parallel to the rows of tubes or tracheids),
and are seen as bands on the radial face and
as rows of pores on the tangential face. These
bands or tiers of cell rows are the medullary
rays or pith rays, and are common to all our
lumber woods.

In the pines and other conifers they are quite
small, but they can readily be seen even without
a magnifier. If a radial surface of split-wood
(not smoothed) is examined, the entire
radial face will be seen almost covered with
these tiny structures, which appear as fine but
conspicuous cross-lines. As shown in Fig. 2, the
cells of the medullary or pith are smaller and
very much shorter than the wood fibre or
tracheids, and their long axis is at right angles
to that of the fiber.

In pines and spruces the cells of the upper
and lower rows of each tier or pith ray have
“bordered” pits, like those of the wood fibre
or tracheids proper, but the cells of the intermediate
rows in the rays of cedars, etc., have
only “simple” pits, i.e., pits devoid of the
saucer-like “border” or rim. In pine, many
of the pith rays are larger than the majority,[16]
each containing a whitish line, the horizontal resin duct,
which, though much smaller, resembles the vertical ducts
on the cross-section. The larger vertical resin ducts are
best observed on removal of the bark from a fresh piece
of white pine cut in the winter where they appear as conspicuous
white lines, extending often for many inches up
and down the stem. Neither the horizontal nor the vertical
resin ducts are vessels or cells, but are openings between
cells, i.e., intercellular spaces, in which the resin accumulates,
freely oozing out when the ducts of a fresh piece of
sapwood are cut. They are present only in our coniferous
woods, and even here they are restricted to pine, spruce,
and larch, and are normally absent in fir, cedar, cypress,
and yew. Altogether, the structure of coniferous woods
is very simple and regular, the bulk being made up of the
small fibres called tracheids, the disturbing elements of
pith rays and resin ducts being insignificant, and hence
the great uniformity and great technical value of coniferous
woods.[17]

Fig. 3. Group of Fibres from Pine Wood. Partly schematic. The little
circles are “border pits” (see Fig. 2, a-c). The transverse rows of
square pits indicate the places of contact of these fibres and the cells
of the neighboring pith rays. Magnified about 25 times.

LIST OF IMPORTANT CONIFEROUS WOODS

CEDAR

Light soft, stiff, not strong, of fine texture. Sap- and
heartwood distinct, the former lighter, the latter a dull
grayish brown or red. The wood seasons rapidly, shrinks
and checks but little, and is very durable in contact with
the soil. Used like soft pine, but owing to its great durability
preferred for shingles, etc. Cedars usually occur
scattered, but they form in certain localities forests of
considerable extent.

(a) White Cedars

1. White Cedar (Thuya occidentalis) (Arborvitæ, Tree of
Life). Heartwood light yellowish brown, sapwood
nearly white. Wood light, soft, not strong, of fine
texture, very durable in contact with the soil, very
fragrant. Scattered along streams and lakes, frequently
covering extensive swamps; rarely large
enough for lumber, but commonly used for fence
posts, rails, railway ties, and shingles. This species
has been extensively cultivated as an ornamental tree
for at least a century. Maine to Minnesota and
northward.

2. Canoe Cedar (Thuya gigantea) (Red Cedar of the West).
In Oregon and Washington a very large tree, covering
extensive swamps; in the mountains much smaller,
skirting the water courses. An important lumber
tree. The wood takes a fine polish; suitable for
interior finishing, as there is much variety of shading
in the color. Washington to northern California
and eastward to Montana.

3. White Cedar (Chamæcyparis thyoides). Medium-sized
tree. Heartwood light brown with rose tinge, sapwood[18]
paler. Wood light, soft, not strong, close-grained,
easily worked, very durable in contact with
the soil and very fragrant. Used in boatbuilding
cooperage, interior finish, fence posts, railway ties,
etc. Along the coast from Maine to Mississippi.

4. White Cedar (Chamæcyparis Lawsoniana) (Port Orford
Cedar, Oregon Cedar, Lawson’s Cypress, Ginger
Pine). A very large tree. A fine, close-grained,
yellowish-white, durable timber, elastic, easily worked,
free of knots, and fragrant. Extensively cut for
lumber; heavier and stronger than any of the preceding.
Along the coast line of Oregon.

5. White Cedar (Libocedrus decurrens) (Incense Cedar).
A large tree, abundantly scattered among pine and
fir. Wood fine-grained. Cascades and Sierra Nevada
Mountains of Oregon and California.

6. Yellow Cedar (Cupressus nootkatensis) (Alaska Cedar,
Alaska Cypress). A very large tree, much used for
panelling and furniture. A fine, close-grained, yellowish
white, durable timber, easily worked. Along
the coast line of Oregon north.

(b) Red Cedars

7. Red Cedar (Juniperus Virginiana) (Savin Juniper,
Juniper, Red Juniper, Juniper Bush, Pencil Cedar).
Heartwood dull red color, thin sapwood nearly white.
Close even grain, compact structure. Wood light,
soft, weak, brittle, easily worked, durable in contact
with the soil, and fragrant. Used for ties, posts,
interior finish, pencil cases, cigar boxes, silos, tanks,
and especially for lead pencils, for which purpose
alone several million feet are cut each year. A small
to medium-sized tree scattered through the forests,
or in the West sparsely covering extensive areas (cedar
brakes). The red cedar is the most widely distributed
conifer of the United States, occurring from the Atlantic
to the Pacific, and from Florida to Minnesota.[19]
Attains a suitable size for lumber only in the Southern,
and more especially the Gulf States.

8. Red Cedar (Juniperus communis) (Ground Cedar).
Small-sized tree, its maximum height being about
25 feet. It is found widely distributed throughout
the Northern hemisphere. Wood in its quality similar
to the preceding. The fruit of this species is gathered
in large quantities and used in the manufacture of
gin; whose peculiar flavor and medicinal properties
are due to the oil of Juniper berries, which is secured
by adding the crushed fruit to undistilled grain spirit,
or by allowing the vapor to pass over it before condensation.
Used locally for construction purposes,
fence posts, etc. Ranges from Greenland to Alaska,
in the East, southward to Pennsylvania and northern
Nebraska; in the Rocky Mountains to Texas, Mexico,
and Arizona.

9. Redwood (Sequoia sempervirens) (Sequoia, California
Redwood, Coast Redwood). Wood in its quality
and uses like white cedar. Thick, red heartwood,
changing to reddish brown when seasoned. Thin
sapwood, nearly white, coarse, straight grain, compact
structure. Light, not strong, soft, very durable in
contact with the soil, not resinous, easily worked,
does not burn easily, receives high polish. Used for
timber, shingles, flumes, fence posts, coffins, railway ties,
water pipes, interior decorations, and cabinetmaking.
A very large tree, limited to the coast ranges of California,
and forming considerable forests, which are
rapidly being converted into lumber.

CYPRESS

10. Cypress (Taxodium distinchum) (Bald Cypress, Black,
White, and Red Cypress, Pecky Cypress). Wood in
its appearance, quality, and uses similar to white
cedar. “Black” and “White Cypress” are heavy
and light forms of the same species. Heartwood
brownish; sapwood nearly white. Wood close,[20]
straight-grain, frequently full of small holes caused by
disease known as “pecky cypress.” Greasy appearance
and feeling. Wood light, soft, not strong,
durable in contact with the soil, takes a fine polish.
Green wood often very heavy. Used for carpentry,
building construction, shingles, cooperage, railway
ties, silos, tanks, vehicles, and washing machines.
The cypress is a large, deciduous tree, inhabiting
swampy lands, and along rivers and coasts of the
Southern parts of the United States. Grows to a
height of 150 feet and 12 feet in diameter.

FIR

This name is frequently applied to wood and to trees
which are not fir; most commonly to spruce, but also,
especially in English markets, to pine. It resembles
spruce, but is easily distinguished from it, as well as from
pine and larch, by the absence of resin ducts. Quality,
uses, and habits similar to spruce.

11. Balsam Fir (Abies balsamea) (Balsam, Fir Tree, Balm
of Gilead Fir). Heartwood white to brownish; sapwood
lighter color; coarse-grained, compact structure,
satiny. Wood light, not durable or strong, resinous,
easily split. Used for boxes, crates, doors, millwork,
cheap lumber, paper pulp. Inferior to white pine
or spruce, yet often mixed and sold with these species
in the lumber market. A medium-sized tree scattered
throughout the northern pineries, and cut in lumber
operations whenever of sufficient size. Minnesota
to Maine and northward.

12. White Fir (Abies grandis and Abies concolor). Medium-
to very large-sized tree, forming an important part of
most of the Western mountain forests, and furnishes
much of the lumber of the respective regions. The
former occurs from Vancouver to California, and the
latter from Oregon to Arizona and eastward to Colorado
and Mexico. The wood is soft and light, coarse-grained,
not unlike the “Swiss pine” of Europe, but[21]
darker and firmer, and is not suitable for any purpose
requiring strength. It is used for boxes, barrels, and
to a small extent for wood pulp.

13. White Fir (Abies amabalis). Good-sized tree, often
forming extensive mountain forests. Wood similar
in quality and uses to Abies grandis. Cascade Mountains
of Washington and Oregon.

14. Red Fir (Abies nobilis) (Noble Fir) (not to be confounded
with Douglas spruce. See No. 40). Large
to very large-sized tree, forming extensive forests on
the slope of the mountains between 3,000 and 4,000
feet elevation. Cascade Mountains of Oregon.

15. Red Fir (Abies magnifica). Very large-sized tree,
forming forests about the base of Mount Shasta.
Sierra Nevada Mountains of California, from Mount
Shasta southward.

HEMLOCK

Light to medium weight, soft, stiff, but brittle, commonly
cross-grained, rough and splintery. Sapwood and heartwood
not well defined. The wood of a light reddish-gray
color, free from resin ducts, moderately durable, shrinks
and warps considerably in drying, wears rough, retains
nails firmly. Used principally for dimension stuff and
timbers. Hemlocks are medium- to large-sized trees,
commonly scattered among broad-leaved trees and conifers,
but often forming forests of almost pure growth.

16. Hemlock (Tsuga canadensis) (Hemlock Spruce,
Peruche). Medium-sized tree, furnishes almost all
the hemlock of the Eastern market. Maine to Wisconsin,
also following the Alleghanies southward to
Georgia and Alabama.

17. Hemlock (Tsuga mertensiana). Large-sized tree,
wood claimed to be heavier and harder than the
Eastern species and of superior quality. Used for
pulp wood, floors, panels, and newels. It is not[22]
suitable for heavy construction, especially where exposed
to the weather, it is straight in grain and will
take a good polish. Not adapted for use partly in
and partly out of the ground; in fresh water as piles
will last about ten years, but as it is softer than fir
it is less able to stand driving successfully. Washington
to California and eastward to Montana.

LARCH or TAMARACK

Wood like the best of hard pine both in appearance,
quality, and uses, and owing to its great durability somewhat
preferred in shipbuilding, for telegraph poles, and
railway ties. In its structure it resembles spruce. The
larches are deciduous trees, occasionally covering considerable
areas, but usually scattered among other conifers.

18. Tamarack (Larix laricina var. Americana) (Larch,
Black Larch, American Larch, Hacmatac). Heartwood
light brown in color, sapwood nearly white,
coarse conspicuous grain, compact structure, annual
rings pronounced. Wood heavy, hard, very strong,
durable in contact with the soil. Used for railway
ties, fence posts, sills, ship timbers, telegraph poles,
flagstaffs. Medium-sized tree, often covering swamps,
in which case it is smaller and of poor quality. Maine
to Minnesota, and southward to Pennsylvania.

19. Tamarack (Larix occidentalis) (Western Larch, Larch).
Large-sized trees, scattered, locally abundant. Is
little inferior to oak in strength and durability.
Heartwood of a light brown color with lighter sapwood,
has a fine, slightly satiny grain, and is
fairly free from knots; the annual rings are distant.
Used for railway ties and shipbuilding. Washington
and Oregon to Montana.

PINE

Very variable, very light and soft in “soft” pine, such
as white pine; of medium weight to heavy and quite
hard in “hard” pine, of which the long-leaf or Georgia[23]
pine is the extreme form. Usually it is stiff, quite strong,
of even texture, and more or less resinous. The sapwood
is yellowish white; the heartwood orange brown. Pine
shrinks moderately, seasons rapidly and without much
injury; it works easily, is never too hard to nail (unlike
oak or hickory); it is mostly quite durable when in contact
with the soil, and if well seasoned is not subject to
the attacks of boring insects. The heavier the wood, the
darker, stronger, and harder it is, and the more it shrinks
and checks when seasoning. Pine is used more extensively
than any other wood. It is the principal wood in
carpentry, as well as in all heavy construction, bridges,
trestles, etc. It is also used in almost every other wood
industry; for spars, masts, planks, and timbers in shipbuilding,
in car and wagon construction, in cooperage and
woodenware; for crates and boxes, in furniture work, for
toys and patterns, water pipes, excelsior, etc. Pines are
usually large-sized trees with few branches, the straight,
cylindrical, useful stem forming by far the greatest part
of the tree. They occur gregariously, forming vast forests,
a fact which greatly facilitates their exploitation. Of the
many special terms applied to pine as lumber, denoting
sometimes differences in quality, the following deserve
attention: “White pine,” “pumpkin pine,” “soft pine,”
in the Eastern markets refer to the wood of the white
pine (Pinus strobus), and on the Pacific Coast to that of
the sugar pine (Pinus lambertiana). “Yellow pine” is
applied in the trade to all the Southern lumber pines; in
the Northwest it is also applied to the pitch pine (Pinus
regida); in the West it refers mostly to the bull pine (Pinus
ponderosa). “Yellow long-leaf pine” (Georgia pine),
chiefly used in advertisements, refers to the long-leaf
Pine (Pinus palustris).

(a) Soft Pines

20. White Pine (Pinus strobus) (Soft Pine, Pumpkin Pine,
Weymouth Pine, Yellow Deal). Large to very large-sized
tree, reaching a height of 80 to 100 feet or more,
and in some instances 7 or 8 feet in diameter. For
the last fifty years the most important timber tree[24]
of the United States, furnishing the best quality of
soft pine. Heartwood cream white; sapwood nearly
white. Close straight grain, compact structure; comparatively
free from knots and resin. Soft, uniform;
seasons well; easy to work; nails without splitting;
fairly durable in contact with the soil; and shrinks
less than other species of pine. Paints well. Used
for carpentry, construction, building, spars, masts,
matches, boxes, etc., etc., etc.

21. Sugar Pine (Pinus lambertiana) (White Pine, Pumpkin
Pine, Soft Pine). A very large tree, forming extensive
forests in the Rocky Mountains and furnishing
most of the timber of the western United States. It
is confined to Oregon and California, and grows at
from 1,500 to 8,000 feet above sea level. Has an
average height of 150 to 175 feet and a diameter of
4 to 5 feet, with a maximum height of 235 feet and 12
feet in diameter. The wood is soft, durable, straight-grained,
easily worked, very resinous, and has a
satiny luster which makes it appreciated for interior
work. It is extensively used for doors, blinds, sashes,
and interior finish, also for druggists’ drawers, owing
to its freedom from odor, for oars, mouldings, shipbuilding,
cooperage, shingles, and fruit boxes. Oregon
and California.

22. White Pine (Pinus monticolo). A large tree, at home
in Montana, Idaho, and the Pacific States. Most
common and locally used in northern Idaho.

23. White Pine (Pinus flexilis). A small-sized tree,
forming mountain forests of considerable extent and
locally used. Eastern Rocky Mountain slopes, Montana
to New Mexico.

(b) Hard Pines

24. Long-Leaf Pine (Pinus palustris) (Georgia Pine,
Southern Pine, Yellow Pine, Southern Hard Pine,
Long-straw Pine, etc.). Large-sized tree. This
species furnishes the hardest and most durable as[25]
well as one of the strongest pine timbers in the market.
Heartwood orange, sapwood lighter color, the annual
rings are strongly marked, and it is full of resinous
matter, making it very durable, but difficult to work.
It is hard, dense, and strong, fairly free from knots,
straight-grained, and one of the best timbers for
heavy engineering work where great strength, long
span, and durability are required. Used for heavy
construction, shipbuilding, cars, docks, beams, ties,
flooring, and interior decoration. Coast region from
North Carolina to Texas.

25. Bull Pine (Pinus ponderosa) (Yellow Pine, Western
Yellow Pine, Western Pine, Western White Pine,
California White Pine). Medium- to very large-sized
tree, forming extensive forests in the Pacific and
Rocky Mountain regions. Heartwood reddish brown,
sapwood yellowish white, and there is often a good
deal of it. The resinous smell of the wood is very
remarkable. It is extensively used for beams, flooring,
ceilings, and building work generally.

26. Bull Pine (Pinus Jeffreyi) (Black Pine). Large-sized
tree, wood resembles Pinus ponderosa and replacing
same at high altitudes. Used locally in
California.

27. Loblolly Pine (Pinus tæda) (Slash Pine, Old Field
Pine, Rosemary Pine, Sap Pine, Short-straw Pine).
A large-sized tree, forms extensive forests. Wider-ringed,
coarser, lighter, softer, with more sapwood
than the long-leaf pine, but the two are often confounded
in the market. The more Northern tree
produces lumber which is weak, brittle, coarse-grained,
and not durable, the Southern tree produces a better
quality wood. Both are very resinous. This is the
common lumber pine from Virginia to South Carolina,
and is found extensively in Arkansas and Texas.
Southern States, Virginia to Texas and Arkansas.

28. Norway Pine (Pinus resinosa) (American Red Pine,
Canadian Pine). Large-sized tree, never forming[26]
forests, usually scattered or in small groves, together
with white pine. Largely sapwood and hence not
durable. Heartwood reddish white, with fine, clear
grain, fairly tough and elastic, not liable to warp and
split. Used for building construction, bridges, piles,
masts, and spars. Minnesota to Michigan; also in
New England to Pennsylvania.

29. Short-Leaf Pine (Pinus echinata) (Slash Pine, Spruce
Pine, Carolina Pine, Yellow Pine, Old Field Pine,
Hard Pine). A medium- to large-sized tree, resembling
loblolly pine, often approaches in its wood the
Norway pine. Heartwood orange, sapwood lighter;
compact structure, apt to be variable in appearance
in cross-section. Wood usually hard, tough, strong,
durable, resinous. A valuable timber tree, sometimes
worked for turpentine. Used for heavy construction,
shipbuilding, cars, docks, beams, ties, flooring, and
house trim. Pinus echinata, palustris, and tæda are
very similar in character, of thin wood and very difficult
to distinguish one from another. As a rule, however,
palustris (Long-leaf Pine) has the smallest and
most uniform growth rings, and Pinus tæda (Loblolly
Pine) has the largest. All are apt to be bunched
together in the lumber market as Southern Hard
Pine. All are used for the same purposes. Short-leaf
is the common lumber pine of Missouri and
Arkansas. North Carolina to Texas and Missouri.

30. Cuban Pine (Pinus cubensis) (Slash Pine, Swamp
Pine, Bastard Pine, Meadow Pine). Resembles long-leaf
pine, but commonly has a wider sapwood and
coarser grain. Does not enter the markets to any
extent. Along the coast from South Carolina to
Louisiana.

31. Pitch Pine (Pinus rigida) (Torch Pine). A small to
medium-sized tree. Heartwood light brown or red,
sapwood yellowish white. Wood light, soft, not
strong, coarse-grained, durable, very resinous. Used
locally for lumber, fuel, and charcoal. Coast regions[27]
from New York to Georgia, and along the mountains
to Kentucky.

32. Black Pine (Pinus murryana) (Lodge-pole Pine,
Tamarack). Small-sized tree. Rocky Mountains
and Pacific regions.

33. Jersey Pine (Pinus inops var. Virginiana) (Scrub
Pine). Small-sized tree. Along the coast from New
York to Georgia and along the mountains to Kentucky.

34. Gray Pine (Pinus divaricata var. banksiana) (Scrub
Pine, Jack Pine). Medium- to large-sized tree.
Heartwood pale brown, rarely yellow; sapwood nearly
white. Wood light, soft, not strong, close-grained.
Used for fuel, railway ties, and fence posts. In days
gone by the Indians preferred this species for frames
of canoes. Maine, Vermont, and Michigan to Minnesota.

REDWOOD (See Cedar)

SPRUCE

Resembles soft pine, is light, very soft, stiff, moderately
strong, less resinous than pine; has no distinct heartwood,
and is of whitish color. Used like soft pine, but also employed
as resonance wood in musical instruments and
preferred for paper pulp. Spruces, like pines, form extensive
forests. They are more frugal, thrive on thinner
soils, and bear more shade, but usually require a more
humid climate. “Black” and “White” spruce as applied
by lumbermen usually refer to narrow and wide-ringed
forms of black spruce (Picea nigra).

35. Black Spruce (Picea nigra var. mariana). Medium-sized
tree, forms extensive forests in northwestern
United States and in British America; occurs scattered
or in groves, especially in low lands throughout
the northern pineries. Important lumber tree in
eastern United States. Heartwood pale, often with
reddish tinge; sapwood pure white. Wood light,[28]
soft, not strong. Chiefly used for manufacture of
paper pulp, and great quantities of this as well as
Picea alba are used for this purpose. Used also for
sounding boards for pianos, violins, etc. Maine to
Minnesota, British America, and in the Alleghanies
to North Carolina.

36. White Spruce (Picea canadensis var. alba). Medium- to
large-sized tree. Heartwood light yellow; sapwood
nearly white. Generally associated with the
preceding. Most abundant along streams and lakes,
grows largest in Montana and forms the most important
tree of the sub-arctic forest of British America.
Used largely for floors, joists, doors, sashes, mouldings,
and panel work, rapidly superceding Pinus strobus
for building purposes. It is very similar to Norway
pine, excels it in toughness, is rather less durable and
dense, and more liable to warp in seasoning. Northern
United States from Maine to Minnesota, also from
Montana to Pacific, British America.

37. White Spruce (Picea engelmanni). Medium- to large-sized
tree, forming extensive forests at elevations
from 5,000 to 10,000 feet above sea level; resembles
the preceding, but occupies a different station. A
very important timber tree in the central and southern
parts of the Rocky Mountains. Rocky Mountains
from Mexico to Montana.

38. Tide-Land Spruce (Picea sitchensis) (Sitka Spruce).
A large-sized tree, forming an extensive coast-belt
forest. Used extensively for all classes of cooperage
and woodenware on the Pacific Coast. Along the
sea-coast from Alaska to central California.

39. Red Spruce (Picea rubens). Medium-sized tree, generally
associated with Picea nigra and occurs scattered
throughout the northern pineries. Heartwood reddish;
sapwood lighter color, straight-grained, compact
structure. Wood light, soft, not strong, elastic,
resonant, not durable when exposed. Used for flooring,
carpentry, shipbuilding, piles, posts, railway[29]
ties, paddles, oars, sounding boards, paper pulp, and
musical instruments. Montana to Pacific, British
America.

BASTARD SPRUCE

Spruce or fir in name, but resembling hard pine or larch
in appearance, quality and uses of its wood.

40. Douglas Spruce (Pseudotsuga douglasii) (Yellow Fir,
Red Fir, Oregon Pine). One of the most important
trees of the western United States; grows very large
in the Pacific States, to fair size in all parts of the
mountains, in Colorado up to about 10,000 feet above
sea level; forms extensive forests, often of pure
growth, it is really neither a pine nor a fir. Wood
very variable, usually coarse-grained and heavy,
with very pronounced summer-wood. Hard and
strong (“red” fir), but often fine-grained and light
(“yellow” fir). It is the chief tree of Washington
and Oregon, and most abundant and most valuable
in British Columbia, where it attains its greatest
size. From the plains to the Pacific Ocean, and from
Mexico to British Columbia.

41. Red Fir (Pseudotsuga taxifolia) (Oregon Pine, Puget
Sound Pine, Yellow Fir, Douglas Spruce, Red Pine).
Heartwood light red or yellow in color, sapwood narrow,
nearly white, comparatively free from resins, variable
annual rings. Wood usually hard, strong, difficult
to work, durable, splinters easily. Used for heavy
construction, dimension timber, railway ties, doors,
blinds, interior finish, piles, etc. One of the most
important of Western trees. From the plains to
the Pacific Ocean, and from Mexico to British America.

TAMARACK (See Larch)

YEW

Wood heavy, hard, extremely stiff and strong, of fine
texture with a pale yellow sapwood, and an orange-red
heartwood; seasons well and is quite durable. Extensively[30]
used for archery bows, turner’s ware, etc. The
yews form no forests, but occur scattered with other
conifers.

42. Yew (Taxus brevifolia). A small to medium-sized
tree of the Pacific region.

SECTION III[31]

BROAD-LEAVED TREES

WOOD OF BROAD-LEAVED TREES

On a cross-section of oak, the same arrangement of pith
and bark, of sapwood and heartwood, and the same disposition
of the wood in well-defined concentric or annual
rings occur, but the rings are marked by lines or rows of
conspicuous pores or openings, which occupy the greater
part of the spring-wood for each ring (see Fig. 4, also 6),
and are, in fact the hollows of vessels
through which the cut has been
made. On the radial section or
quarter-sawn board the several
layers appear as so many stripes
(see Fig. 5); on the tangential section
or “bastard” face patterns
similar to those mentioned for pine
wood are observed. But while the
patterns in hard pine are marked
by the darker summer-wood, and
are composed of plain, alternating
stripes of darker and lighter wood,
the figures in oak (and other broad-leaved
woods) are due chiefly to
the vessels, those of the spring-wood
in oak being the most
conspicuous (see Fig. 5). So that in an oak table, the
darker, shaded parts are the spring-wood, the lighter
unicolored parts the summer-wood. On closer examination
of the smooth cross-section of oak, the spring-wood
part of the ring is found to be formed in great part
of pores; large, round, or oval openings made by the cut
through long vessels. These are separated by a grayish[32]
and quite porous tissue (see Fig. 6, A), which continues
here and there in the form of radial, often branched,
patches (not the pith rays) into and through the summer-wood
to the spring-wood of the next ring. The large
vessels of the spring-wood, occupying six to ten per cent
of the volume of a log in very good oak, and twenty-five
per cent or more in inferior and narrow-ringed timber,
are a very important feature, since it is evident that the
greater their share in the volume, the lighter and weaker
the wood. They are smallest near the pith, and grow
wider outward. They are wider in the stem than limb,
and seem to be of indefinite length, forming open channels,
in some cases probably as long
as the tree itself. Scattered
through the radiating gray
patches of porous wood are
vessels similar to those of the[33]
spring-wood, but decidedly
smaller. These vessels are
usually fewer and larger near
the outer portions of the ring.
Their number and size can be
utilized to distinguish the oaks
classed as white oaks from
those classed as black and
red oaks. They are fewer and
larger in red oaks, smaller but
much more numerous in white
oaks. The summer-wood,
except for these radial, grayish patches, is dark colored and
firm. This firm portion, divided into bodies or strands by
these patches of porous wood, and also by fine, wavy, concentric
lines of short, thin-walled cells (see Fig. 6, A), consists
of thin-walled fibres (see Fig. 7, B), and is the chief element
of strength in oak wood. In good white oak it forms
one-half or more of the wood, if it cuts like horn, and the
cut surface is shiny, and of a deep chocolate brown color.
In very narrow-ringed wood and in inferior red oak it is
usually much reduced in quantity as well as quality. The
pith rays of the oak, unlike those of the coniferous woods,[34]
are at least in part very large and conspicuous. (See Fig.
4; their height indicated by the letter a, and their width
by the letter b.) The large medullary rays of oak are
often twenty and more cells wide, and several hundred
cell rows in height, which amount
commonly to one or more inches.
These large rays are conspicuous
on all sections. They appear as
long, sharp, grayish lines on the
cross-sections; as short, thick lines,
tapering at each end, on the tangential
or “bastard” face, and as
broad, shiny bands, “the mirrors,”
on the radial section. In addition
to these coarse rays, there is also
a large number of small pith rays,
which can be seen only when magnified.
On the whole, the pith
rays form a much larger part of
the wood than might be supposed.
In specimens of good white oak it
has been found that they form
about sixteen to twenty-five per
cent of the wood.

Fig. 8. Isolated Fibres and
Cells, a, four cells of
wood, parenchyma; b,
two cells from a pith ray;
c, a single joint or cell of
a vessel, the openings x
leading into its upper
and lower neighbors; d,
tracheid; e, wood fibre
proper.

Minute Structure

If a well-smoothed thin disk or
cross-section of oak (say one-sixteenth
inch thick) is held up to
the light, it looks very much like
a sieve, the pores or vessels appearing
as clean-cut holes. The
spring-wood and gray patches are
seen to be quite porous, but the
firm bodies of fibres between them
are dense and opaque. Examined
with a magnifier it will be noticed
that there is no such regularity of arrangement in straight
rows as is conspicuous in pine. On the contrary, great
irregularity prevails. At the same time, while the pores[35]
are as large as pin holes, the cells of the denser wood,
unlike those of pine wood, are too small to be distinguished.
Studied with the microscope, each vessel is
found to be a vertical row of a great number of short,
wide tubes, joined end to end (see Fig. 8, c). The
porous spring-wood and radial gray tracts are partly
composed of smaller vessels, but chiefly of tracheids, like
those of pine, and of shorter cells, the “wood parenchyma,”
resembling the cells of the medullary rays. These latter,
as well as the fine concentric lines mentioned as occurring
in the summer-wood, are composed entirely of short tube-like
parenchyma cells, with square or oblique ends (see
Fig. 8, a and b). The wood fibres proper, which form the
dark, firm bodies referred to, are very fine, thread-like
cells, one twenty-fifth to one-tenth inch long, with a wall
commonly so thick that scarcely any empty internal space
or lumen remains (see Figs. 8, e, and 7, B). If, instead
of oak, a piece of poplar or basswood (see Fig. 9)
had been used in this study, the structure would have
been found to be quite different. The same kinds of cell-elements,
vessels, etc., are, to be sure, present, but their
combination and arrangement are different, and thus
from the great variety of possible combinations results
the great variety of structure and, in consequence, of
the qualities which distinguish the wood of broad-leaved
trees. The sharp distinction of sap wood and heartwood
is wanting; the rings are not so clearly defined; the vessels[36]
of the wood are small, very numerous, and rather evenly
scattered through the wood of the annual rings, so that
the distinction of the ring almost vanishes and the medullary
or pith rays in poplar can be seen, without being
magnified, only on the radial section.

LIST OF MOST IMPORTANT BROAD-LEAVED
TREES (HARDWOODS)[37]

Woods of complex and very variable structure, and
therefore differing widely in quality, behavior, and consequently
in applicability to the arts.

AILANTHUS

1. Ailanthus (Ailanthus glandulosa). Medium to large-sized
tree. Wood pale yellow, hard, fine-grained, and
satiny. This species originally came from China,
where it is known as the Tree of “Heaven,” was introduced
into the United States and planted near
Philadelphia during the 18th century, and is more
ornamental than useful. It is used to some extent
in cabinet work. Western Pennsylvania and Long
Island, New York.

ASH

Wood heavy, hard, stiff, quite tough, not durable in
contact with the soil, straight-grained, rough on the split
surfaces and coarse in texture. The wood shrinks moderately,
seasons with little injury, stands well, and takes a
good polish. In carpentry, ash is used for stairways,
panels, etc. It is used in shipbuilding, in the construction
of cars, wagons, etc., in the manufacture of all kinds of
farm implements, machinery, and especially of all kinds
of furniture; for cooperage, baskets, oars, tool handles,
hoops, etc., etc. The trees of the several species of ash
are rapid growers, of small to medium height with stout
trunks. They form no forests, but occur scattered in
almost all our broad-leaved forests.

2. White Ash (Fraxinus Americana). Medium-, sometimes
large-sized tree. Heartwood reddish brown,
usually mottled; sapwood lighter color, nearly white.
Wood heavy, hard, tough, elastic, coarse-grained,[38]
compact structure. Annual rings clearly marked by
large open pores, not durable in contact with the
soil, is straight-grained, and the best material for oars,
etc. Used for agricultural implements, tool handles,
automobile (rim boards), vehicle bodies and parts,
baseball bats, interior finish, cabinet work, etc., etc.
Basin of the Ohio, but found from Maine to Minnesota
and Texas.

3. Red Ash (Fraxinus pubescens var. Pennsylvanica).
Medium-sized tree, a timber very similar to, but
smaller than Fraxinus Americana. Heartwood light
brown, sapwood lighter color. Wood heavy, hard,
strong, and coarse-grained. Ranges from New
Brunswick to Florida, and westward to Dakota,
Nebraska, and Kansas.

4. Black Ash (Fraxinus nigra var. sambucifolia) (Hoop
Ash, Ground Ash). Medium-sized tree, very common,
is more widely distributed than the Fraxinus Americana;
the wood is not so hard, but is well suited for
hoops and basketwork. Heartwood dark brown,
sapwood light brown or white. Wood heavy, rather
soft, tough and coarse-grained. Used for barrel
hoops, basketwork, cabinetwork and interior of
houses. Maine to Minnesota and southward to
Alabama.

5. Blue Ash (Fraxinus quadrangulata). Small to medium-sized
tree. Heartwood yellow, streaked with brown,
sapwood a lighter color. Wood heavy, hard, and
coarse-grained. Not common. Indiana and Illinois;
occurs from Michigan to Minnesota and southward
to Alabama.

6. Green Ash (Fraxinus viridis). Small-sized tree. Occurs
from New York to the Rocky Mountains, and
southward to Florida and Arizona.

7. Oregon Ash (Fraxinus Oregana). Small to medium-sized
tree. Occurs from western Washington to
California.[39]

8. Carolina Ash (Fraxinus Caroliniana). Medium-sized
tree. Occurs in the Carolinas and the coast regions
southward.

ASPEN (See Poplar)

BASSWOOD

9. Basswood (Tilia Americana) (Linden, Lime Tree,
American Linden, Lin, Bee Tree). Medium- to large-sized
tree. Wood light, soft, stiff, but not strong,
of fine texture, straight and close-grained, and white
to light brown color, but not durable in contact with
the soil. The wood shrinks considerably in drying,
works well and stands well in interior work. It is
used for cooperage, in carpentry, in the manufacture
of furniture and woodenware (both turned and carved),
for toys, also for panelling of car and carriage bodies,
for agricultural implements, automobiles, sides and
backs of drawers, cigar boxes, excelsior, refrigerators,
trunks, and paper pulp. It is also largely cut for
veneer and used as “three-ply” for boxes and chair
seats. It is used for sounding boards in pianos and
organs. If well seasoned and painted it stands fairly
well for outside work. Common in all northern
broad-leaved forests. Found throughout the eastern
United States, but reaches its greatest size in the
Valley of the Ohio, becoming often 130 feet in height,
but its usual height is about 70 feet.

10. White Basswood (Tilia heterophylla) (Whitewood).
A small-sized tree. Wood in its quality and uses
similar to the preceding, only it is lighter in color.
Most abundant in the Alleghany region.

11. White Basswood (Tilia pubescens) (Downy Linden,
Small-leaved Basswood). Small-sized tree. Wood
in its quality and uses similar to Tilia Americana.
This is a Southern species which makes it way as far
north as Long Island. Is found at its best in South
Carolina.[40]

BEECH

12. Beech (Fagus ferruginea) (Red Beech, White Beech).
Medium-sized tree, common, sometimes forming
forests of pure growth. Wood heavy, hard, stiff,
strong, of rather coarse texture, white to light brown
color, not durable in contact with the soil, and subject
to the inroads of boring insects. Rather close-grained,
conspicuous medullary rays, and when
quarter-sawn and well smoothed is very beautiful.
The wood shrinks and checks considerably in drying,
works well and stands well, and takes a fine polish.
Beech is comparatively free from objectionable taste,
and finds a place in the manufacture of commodities
which come in contact with foodstuffs, such as lard
tubs, butter boxes and pails, and the beaters of ice
cream freezers; for the latter the persistent hardness
of the wood when subjected to attrition and abrasion,
while wet gives it peculiar fitness. It is an excellent
material for churns. Sugar hogsheads are made of
beech, partly because it is a tasteless wood and partly
because it has great strength. A large class of woodenware,
including veneer plates, dishes, boxes, paddles,
scoops, spoons, and beaters, which belong to the
kitchen and pantry, are made of this species of wood.
Beech picnic plates are made by the million, a single
machine turning out 75,000 a day. The wood has
a long list of miscellaneous uses and enters in
a great variety of commodities. In every region
where it grows in commercial quantities it is made
into boxes, baskets, and crating. Beech baskets are
chiefly employed in shipping fruit, berries, and vegetables.
In Maine thin veneer of beech is made
specially for the Sicily orange and lemon trade. This
is shipped in bulk and the boxes are made abroad.
Beech is also an important handle wood, although
not in the same class with hickory. It is not selected
because of toughness and resiliency, as hickory is,
and generally goes into plane, handsaw, pail, chisel,[41]
and flatiron handles. Recent statistics show that
in the production of slack cooperage staves, only
two woods, red gum and pine, stood above beech in
quantity, while for heading, pine alone exceeded it.
It is also used in turnery, for shoe lasts, butcher
blocks, ladder rounds, etc. Abroad it is very extensively
used by the carpenter, millwright, and wagon
maker, in turnery and wood carving. Most abundant
in the Ohio and Mississippi basin, but found from
Maine to Wisconsin and southward to Florida.

BIRCH

13. Cherry Birch (Betula lenta) (Black Birch, Sweet Birch,
Mahogany Birch, Wintergreen Birch). Medium-sized
tree, very common. Wood of beautiful reddish
or yellowish brown, and much of it nicely figured,
of compact structure, is straight in grain, heavy,
hard, strong, takes a fine polish, and considerably used
as imitation of mahogany. The wood shrinks considerably
in drying, works well and stands well, but
is not durable in contact with the soil. The medullary
rays in birch are very fine and close and not
easily seen. The sweet birch is very handsome, with
satiny luster, equalling cherry, and is too costly a
wood to be profitably used for ordinary purposes,
but there are both high and low grades of birch, the
latter consisting chiefly of sapwood and pieces too
knotty for first class commodities. This cheap material
swells the supply of box lumber, and a little of
it is found wherever birch passes through sawmills.
The frequent objections against sweet birch as box
lumber and crating material are that it is hard to
nail and is inclined to split. It is also used for veneer
picnic plates and butter dishes, although it is not
as popular for this class of commodity as are yellow
and paper birch, maple and beech. The best grades
are largely used for furniture and cabinet work, and
also for interior finish. Maine to Michigan and to
Tennessee.[42]

14. White Birch (Betula populifolia) (Gray Birch, Old
Field Birch, Aspen-leaved Birch). Small to medium-sized
tree, least common of all the birches. Short-lived,
twenty to thirty feet high, grows very rapidly.
Heartwood light brown, sapwood lighter color. Wood
light, soft, close-grained, not strong, checks badly
in drying, decays quickly, not durable in contact
with the soil, takes a good polish. Used for spools,
shoepegs, wood pulp, and barrel hoops. Fuel, value
not high, but burns with bright flame. Ranges from
Nova Scotia and lower St. Lawrence River, southward,
mostly in the coast region to Delaware, and
westward through northern New England and New
York to southern shore of Lake Ontario.

15. Yellow Birch (Betula lutea) (Gray Birch, Silver Birch).
Medium- to large-sized tree, very common. Heartwood
light reddish brown, sapwood nearly white,
close-grained, compact structure, with a satiny luster.
Wood heavy, very strong, hard, tough, susceptible
of high polish, not durable when exposed. Is similar
to Betula lenta, and finds a place in practically all
kinds of woodenware. A large percentage of broom
handles on the market are made of this species of
wood, though nearly every other birch contributes
something. It is used for veneer plates and dishes
made for pies, butter, lard, and many other commodities.
Tubs and pails are sometimes made of
yellow birch provided weight is not objectionable.
The wood is twice as heavy as some of the pines and
cedars. Many small handles for such articles as
flatirons, gimlets, augers, screw drivers, chisels, varnish
and paint brushes, butcher and carving knives,
etc. It is also widely used for shipping boxes, baskets,
and crates, and it is one of the stiffest, strongest
woods procurable, but on account of its excessive
weight it is sometimes discriminated against. It
is excellent for veneer boxes, and that is probably
one of the most important places it fills. Citrus
fruit from northern Africa and the islands and countries
of the Mediterranean is often shipped to market[43]
in boxes made of yellow birch from veneer cut in
New England. The better grades are also used for
furniture and cabinet work, and the “burls” found
on this species are highly valued for making fancy
articles, gavels, etc. It is extensively used for turnery,
buttons, spools, bobbins, wheel hubs, etc. Maine
to Minnesota and southward to Tennessee.

16. Red Birch (Betula rubra var. nigra) (River Birch).
Small to medium-sized tree, very common. Lighter
and less valuable than the preceding. Heartwood
light brown, sapwood pale. Wood light, fairly strong
and close-grained. Red birch is best developed in
the middle South, and usually grows near the banks
of rivers. Its bark hangs in tatters, even worse than
that of paper birch, but it is darker. In Tennessee
the slack coopers have found that red birch makes
excellent barrel heads and it is sometimes employed
in preference to other woods. In eastern Maryland
the manufacturers of peach baskets draw their supplies
from this wood, and substitute it for white elm
in making the hoops or bands which stiffen the top
of the basket, and provide a fastening for the veneer
which forms the sides. Red birch bends in a very
satisfactory manner, which is an important point.
This wood enters pretty generally into the manufacture
of woodenware within its range, but statistics
do not mention it by name. It is also used in the
manufacture of veneer picnic plates, pie plates, butter
dishes, washboards, small handles, kitchen and pantry
utensils, and ironing boards. New England to Texas
and Missouri.

17. Canoe Birch (Betula paprifera) (White Birch, Paper
Birch). Small to medium-sized tree, sometimes forming
forests, very common. Heartwood light brown
tinged with red, sapwood lighter color. Wood of
good quality, but light, fairly hard and strong, tough,
close-grained. Sap flows freely in spring and by
boiling can be made into syrup. Not as valuable as
any of the preceding. Canoe birch is a northern[44]
tree, easily identified by its white trunk and its ragged
bark. Large numbers of small wooden boxes are
made by boring out blocks of this wood, shaping
them in lathes, and fitting lids on them. Canoe
birch is one of the best woods for this class of commodities,
because it can be worked very thin, does
not split readily, and is of pleasing color. Such boxes,
or two-piece diminutive kegs, are used as containers
for articles shipped and sold in small bulk, such as
tacks, small nails, and brads. Such containers are
generally cylindrical and of considerably greater depth
than diameter. Many others of nearly similar form
are made to contain ink bottles, bottles of perfumery,
drugs, liquids, salves, lotions, and powders of many
kinds. Many boxes of this pattern are used by
manufacturers of pencils and crayons for packing
and shipping their wares. Such boxes are made in
numerous numbers by automatic machinery. A
single machine of the most improved pattern will
turn out 1,400 boxes an hour. After the boring and
turning are done, they are smoothed by placing them
into a tumbling barrel with soapstone. It is also
used for one-piece shallow trays or boxes, without
lids, and used as card receivers, pin receptacles,
butter boxes, fruit platters, and contribution plates
in churches. It is also the principal wood used for
spools, bobbins, bowls, shoe lasts, pegs, and turnery,
and is also much used in the furniture trade. All
along the northern boundary of the United States
and northward, from the Atlantic to the Pacific.

BLACK WALNUT (See Walnut)

BLUE BEECH

18. Blue Beech (Carpinus Caroliniana) (Hornbeam, Water
Beech, Ironwood). Small-sized tree. Heartwood
light brown, sapwood nearly white. Wood very hard,
heavy, strong, very stiff, of rather fine texture, not
durable in contact with the soil, shrinks and checks
considerably in drying, but works well and stands[45]
well, and takes a fine polish. Used chiefly in turnery,
for tool handles, etc. Abroad much used by mill-
and wheelwrights. A small tree, largest in the Southwest,
but found in nearly all parts of the eastern
United States.

BOIS D’ARC (See Osage Orange)

BUCKEYE

Wood light, soft, not strong, often quite tough, of fine,
uniform texture and creamy white color. It shrinks considerably
in drying, but works well and stands well. Used
for woodenware, artificial limbs, paper pulp, and locally
also for building construction.

19. Ohio Buckeye (Æsculus glabra) (Horse Chestnut,
Fetid Buckeye). Small-sized tree, scattered, never
forming forests. Heartwood white, sapwood pale
brown. Wood light, soft, not strong, often quite
tough and close-grained. Alleghanies, Pennsylvania
to Oklahoma.

20. Sweet Buckeye (Æsculus octandra var. flava) (Horse
Chestnut). Small-sized tree, scattered, never forming
forests. Wood in its quality and uses similar to
the preceding. Alleghanies, Pennsylvania to Texas.

BUCKTHORNE

21. Buckthorne (Rhanmus Caroliniana) (Indian Cherry).
Small-sized tree. Heartwood light brown, sapwood
almost white. Wood light, hard, close-grained. Does
not enter the markets to any great extent. Found
along the borders of streams in rich bottom lands.
Its northern limits is Long Island, where it is only
a shrub; it becomes a tree only in southern Arkansas
and adjoining regions.

BUTTERNUT

22. Butternut (Juglans cinerea) (White Walnut, White
Mahogany, Walnut). Medium-sized tree, scattered,[46]
never forming forests. Wood very similar to black
walnut, but light, quite soft, and not strong. Heartwood
light gray-brown, darkening with exposure;
sapwood nearly white, coarse-grained, compact structure,
easily worked, and susceptible to high polish.
Has similar grain to black walnut and when stained
is a very good imitation. Is much used for inside
work, and very durable. Used chiefly for finishing
lumber, cabinet work, boat finish and fixtures, and
for furniture. Butternut furniture is often sold as
circassian walnut. Largest and most common in the
Ohio basin. Maine to Minnesota and southward
to Georgia and Alabama.

CATALPA

The catalpa is a tree which was planted about 25 years
ago as a commercial speculation in Iowa, Kansas, and
Nebraska. Its native habitat was along the rivers Ohio
and lower Wabash, and a century ago it gained a reputation
for rapid growth and durability, but did not grow
in large quantities. As a railway tie, experiments have
left no doubt as to its resistance to decay; it stands abrasion
as well as the white oak (Quercus alba), and is
superior to it in longevity. Catalpa is a tree singularly
free from destructive diseases. Wood cut from the living
tree is one of the most durable timbers known. In spite
of its light porous structure it resists the weathering influences
and the attacks of wood-destroying fungi to a
remarkable degree. No fungus has yet been found which
will grow in the dead timber, and for fence posts this wood
has no equal, lasting longer than almost any other species
of timber. The wood is rather soft and coarse in texture,
the tree is of slow growth, and the brown colored heartwood,
even of very young trees, forms nearly three-quarters of
their volume. There is only about one-quarter inch of
sapwood in a 9-inch tree.

23. Catalpa (Catalpa speciosa var. bignonioides) (Indian
Bean). Medium-sized tree. Heartwood light brown,
sapwood nearly white. Wood light, soft, not strong,[47]
brittle, very durable in contact with the soil, of coarse
texture. Used chiefly for railway ties, telegraph poles,
and fence posts, but well suited for a great variety of
uses. Lower basin of the Ohio River, locally common.
Extensively planted, and therefore promising
to become of some importance.

CHERRY

24. Cherry (Prunus serotina) (Wild Cherry, Black Cherry,
Rum Cherry). Wood heavy, hard, strong, of fine
texture. Sapwood yellowish white, heartwood reddish
to brown. The wood shrinks considerably in drying,
works well and stands well, has a fine satin-like luster,
and takes a fine polish which somewhat resembles
mahogany, and is much esteemed for its beauty.
Cherry is chiefly used as a decorative interior finishing
lumber, for buildings, cars and boats, also for
furniture and in turnery, for musical instruments,
walking sticks, last blocks, and woodenware. It is
becoming too costly for many purposes for which it
is naturally well suited. The lumber-furnishing
cherry of the United States, the wild black cherry,
is a small to medium-sized tree, scattered through
many of the broad-leaved trees of the western slope
of the Alleghanies, but found from Michigan to
Florida, and west to Texas. Other species of this
genus, as well as the hawthornes (Prunus cratoegus)
and wild apple (Pyrus), are not commonly offered in
the markets. Their wood is of the same character
as cherry, often finer, but in smaller dimensions.

25. Red Cherry (Prunus Pennsylvanica) (Wild Red Cherry,
Bird Cherry). Small-sized tree. Heartwood light
brown, sapwood pale yellow. Wood light, soft, and
close-grained. Uses similiar to the preceding, common
throughout the Northern States, reaching its
greatest size on the mountains of Tennessee.[48]

CHESTNUT

The chestnut is a long-lived tree, attaining an age of
from 400 to 600 years, but trees over 100 years are usually
hollow. It grows quickly, and sprouts from a chestnut
stump (Coppice Chestnut) often attain a height of 8 feet
in the first year. It has a fairly cylindrical stem, and
often grows to a height of 100 feet and over. Coppice
chestnut, that is, chestnut grown on an old stump, furnishes
better timber for working than chestnut grown from the
nut, it is heavier, less spongy, straighter in grain, easier
to split, and stands exposure longer.

26. Chestnut (Castanea vulgaris var. Americana). Medium-
to large-sized tree, never forming forests. Wood
is light, moderately hard, stiff, elastic, not strong,
but very durable when in contact with the soil, of
coarse texture. Sapwood light, heartwood darker
brown, and is readily distinguishable from the sapwood,
which very early turns into heartwood. It
shrinks and checks considerably in drying, works
easily, stands well. The annual rings are very distinct,
medullary rays very minute and not visible to
the naked eye. Used in cooperage, for cabinetwork,
agricultural implements, railway ties, telegraph poles,
fence posts, sills, boxes, crates, coffins, furniture,
fixtures, foundation for veneer, and locally in heavy
construction. Very common in the Alleghanies. Occurs
from Maine to Michigan and southward to
Alabama.

27. Chestnut (Castanea dentata var. vesca). Medium-sized
tree, never forming forests, not common.
Heartwood brown color, sapwood lighter shade,
coarse-grained. Wood and uses similar to the preceding.
Occurs scattered along the St. Lawrence River,
and even there is met with only in small quantities.

28. Chinquapin (Castanea pumila). Medium- to small-sized
tree, with wood slightly heavier, but otherwise
similiar to the preceding. Most common in Arkansas,
but with nearly the same range as Castanea vulgaris.[49]

29. Chinquapin (Castanea chrysophylla). A medium-sized
tree of the western ranges of California and Oregon.

COFFEE TREE

30. Coffee Tree (Gymnocladus dioicus) (Coffee Nut,
Stump Tree). A medium- to large-sized tree, not
common. Wood heavy, hard, strong, very stiff, of
coarse texture, and durable. Sapwood yellow, heartwood
reddish brown, shrinks and checks considerably
in drying, works well and stands well, and takes a
fine polish. It is used to a limited extent in cabinetwork
and interior finish. Pennsylvania to Minnesota
and Arkansas.

COTTONWOOD (See Poplar)

CRAB APPLE

31. Crab Apple (Pyrus coronaria) (Wild Apple, Fragrant
Crab). Small-sized tree. Heartwood reddish brown,
sapwood yellow. Wood heavy, hard, not strong,
close-grained. Used principally for tool handles and
small domestic articles. Most abundant in the middle
and western states, reaches its greatest size in the
valleys of the lower Ohio basin.

CUCUMBER TREE (See Magnolia)

DOGWOOD

32. Dogwood (Cornus florida) (American Box). Small to
medium-sized tree. Attains a height of about 30
feet and about 12 inches in diameter. The heartwood
is a red or pinkish color, the sapwood, which is
considerable, is a creamy white. The wood has a
dull surface and very fine grain. It is valuable for
turnery, tool handles, and mallets, and being so free
from silex, watchmakers use small splinters of it for
cleaning out the pivot holes of watches, and opticians
for removing dust from deep-seated lenses. It is[50]
also used for butchers’ skewers, and shuttle blocks
and wheel stock, and is suitable for turnery and inlaid
work. Occurs scattered in all the broad-leaved forests
of our country; very common.

ELM

Wood heavy, hard, strong, elastic, very tough, moderately
durable in contact with the soil, commonly cross-grained,
difficult to split and shape, warps and checks
considerably in drying, but stands well if properly seasoned.
The broad sapwood whitish, heartwood light brown, both
with shades of gray and red. On split surfaces rough,
texture coarse to fine, capable of high polish. Elm for
years has been the principal wood used in slack cooperage
for barrel staves, also in the construction of cars, wagons,
etc., in boat building, agricultural implements and machinery,
in saddlery and harness work, and particularly
in the manufacture of all kinds of furniture, where
the beautiful figures, especially those of the tangential or
bastard section, are just beginning to be appreciated.
The elms are medium- to large-sized trees, of fairly rapid
growth, with stout trunks; they form no forests of pure
growth, but are found scattered in all the broad-leaved
woods of our country, sometimes forming a considerable
portion of the arborescent growth.

33. White Elm (Ulmus Americana) (American Elm, Water
Elm). Medium- to large-sized tree. Wood in its
quality and uses as stated above. Common. Maine
to Minnesota, southward to Florida and Texas.

34. Rock Elm (Ulmus racemosa) (Cork Elm, Hickory Elm,
White Elm, Cliff Elm). Medium- to large-sized tree
of rapid growth. Heartwood light brown, often
tinged with red, sapwood yellowish or greenish white,
compact structure, fibres interlaced. Wood heavy,
hard, very tough, strong, elastic, difficult to split,
takes a fine polish. Used for agricultural implements,
automobiles, crating, boxes, cooperage, tool
handles, wheel stock, bridge timbers, sills, interior[51]
finish, and maul heads. Fairly free from knots and
has only a small quantity of sapwood. Michigan,
Ohio, from Vermont to Iowa, and southward to
Kentucky.

35. Red Elm (Ulmus fulva var. pubescens) (Slippery Elm,
Moose Elm). The red or slippery elm is not as large
a tree as the white elm (Ulmus Americana), though
it occasionally attains a height of 135 feet and a diameter
of 4 feet. It grows tall and straight, and
thrives in river valleys. The wood is heavy, hard,
strong, tough, elastic, commonly cross-grained, moderately
durable in contact with the soil, splits easily
when green, works fairly well, and stands well if
properly handled. Careful seasoning and handling
are essential for the best results. Trees can be
utilized for posts when very small. When green the
wood rots very quickly in contact with the soil.
Poles for posts should be cut in summer and peeled
and dried before setting. The wood becomes very
tough and pliable when steamed, and is of value for
sleigh runners and for ribs of canoes and skiffs. Together
with white elm (Ulmus Americana) it is extensively
used for barrel staves in slack cooperage
and also for furniture. The thick, viscous inner
bark, which gives the tree its descriptive name, is
quite palatable, slightly nutritious, and has a medicinal
value. Found chiefly along water courses.
New York to Minnesota, and southward to Florida
and Texas.

36. Cedar Elm (Ulmus crassifolia). Medium- to small-sized
tree, locally quite common. Arkansas and
Texas.

37. Winged Elm (Ulmus alata) (Wahoo). Small-sized
tree, locally quite common. Heartwood light brown,
sapwood yellowish white. Wood heavy, hard, tough,
strong, and close-grained. Arkansas, Missouri, and
eastern Virginia.[52]

GUM

This general term applies to three important species
of gum in the South, the principal one usually being distinguished
as “red” or “sweet” gum (see Fig. 10).
The next in importance being the “tupelo” or “bay poplar,”
and the least of the trio is designated as “black” or
“sour” gum (see Fig. 11). Up to the year 1900 little
was known of gum as a wood for cooperage purposes, but[53]
by the continued advance in price of the woods used, a
few of the most progressive manufacturers, looking into
the future, saw that the supply of the various woods in
use was limited, that new woods would have to be sought,
and gum was looked upon as a possible substitute, owing
to its cheapness and abundant supply. No doubt in the
future this wood will be used to a considerable extent in
the manufacture of both “tight” and “slack” cooperage.[54]
In the manufacture of the gum, unless the knives and
saws are kept very sharp, the wood has a tendency to
break out, the corners splitting off; and also, much difficulty
has been experienced in seasoning and kiln-drying.

In the past, gum, having no marketable value, has been
left standing after logging operations, or, where the land
has been cleared for farming, the trees have been “girdled”
and allowed to rot, and then felled and burned as trash.
Now, however, that there is a market for this species of
timber, it will be profitable to cut the gum with the other
hardwoods, and this species of wood will come in for a
greater share of attention than ever before.

38. Red Gum (Liquidamber styraciflua) (Sweet Gum,
Hazel Pine, Satin Walnut, Liquidamber, Bilsted).
The wood is about as stiff and as strong as chestnut,
rather heavy, it splits easily and is quite brash, commonly
cross-grained, of fine texture, and has a large
proportion of whitish sapwood, which decays rapidly
when exposed to the weather; but the reddish brown
heartwood is quite durable, even in the ground. The
external appearance of the wood is of fine grain and
smooth, close texture, but when broken the lines of
fracture do not run with apparent direction of the
growth; possibly it is this unevenness of grain which
renders the wood so difficult to dry without twisting
and warping. It has little resiliency; can be easily
bent when steamed, and when properly dried will
hold its shape. The annual rings are not distinctly
marked, medullary rays fine and numerous. The
green wood contains much water, and consequently is
heavy and difficult to float, but when dry it is as light
as basswood. The great amount of water in the
green wood, particularly in the sap, makes it difficult
to season by ordinary methods without warping and
twisting. It does not check badly, is tasteless and
odorless, and when once seasoned, swells and shrinks
but little unless exposed to the weather. Used for
boat finish, veneers, cabinet work, furniture, fixtures,
interior decoration, shingles, paving blocks, woodenware,[55]
cooperage, machinery frames, refrigerators, and
trunk slats.

Range of Red Gum

Red gum is distributed from Fairfield County, Conn.,
to southeastern Missouri, through Arkansas and Oklahoma
to the valley of the Trinity River in Texas,
and eastward to the Atlantic coast. Its commercial
range is restricted, however, to the moist lands of
the lower Ohio and Mississippi basins and of the Southeastern
coast. It is one of the commonest timber trees
in the hardwood bottoms and drier swamps of the South.
It grows in mixture with ash, cottonwood and oak (see
Fig. 12). It is also found to a considerable extent on
the lower ridges and slopes of the southern Appalachians,
but there it does not reach merchantable value and is of
little importance. Considerable difference is found between
the growth in the upper Mississippi bottoms and
that along the rivers on the Atlantic coast and on the
Gulf. In the latter regions the bottoms are lower, and
consequently more subject to floods and to continued
overflows (see Fig. 11). The alluvial deposit is also greater,
and the trees grow considerably faster. Trees of the same
diameter show a larger percentage of sapwood there than
in the upper portions of the Mississippi Valley. The
Mississippi Valley hardwood trees are for the most part
considerably older, and reach larger dimensions than the
timber along the coast.

Form of the Red Gum

In the best situations red gum reaches a height of 150
feet, and a diameter of 5 feet. These dimensions, however
are unusual. The stem is straight and cylindrical,
with dark, deeply-furrowed bark, and branches often
winged with corky ridges. In youth, while growing vigorously
under normal conditions, it assumes a long, regular,
conical crown, much resembling the form of a conifer
(see Fig. 12). After the tree has attained its height
growth, however, the crown becomes rounded, spreading
and rather ovate in shape. When growing in the forest[56]
the tree prunes itself readily at an early period, and forms
a good length of clear stem, but it branches strongly after
making most of its height growth. The mature tree is
usually forked, and the place where the forking commences
determines the number of logs in the tree or its merchantable
length, by preventing cutting to a small diameter in
the top. On large trees the stem is often not less than
eighteen inches in diameter where the branching begins.
The over-mature tree is usually broken and dry topped,
with a very spreading crown, in consequence of new
branches being sent out.

Tolerance of Red Gum

Throughout its entire life red gum is intolerant in shade,
there are practically no red seedlings under the dense
forest cover of the bottom land, and while a good many
may come up under the pine forest on the drier uplands,
they seldom develop into large trees. As a rule seedlings
appear only in clearings or in open spots in the forest. It
is seldom that an over-topped tree is found, for the gum
dies quickly if suppressed, and is consequently nearly
always a dominant or intermediate tree. In a hardwood
bottom forest the timber trees are all of nearly the same
age over considerable areas, and there is little young
growth to be found in the older stands. The reason for
this is the intolerance of most of the swamp species. A
scale of intolerance containing the important species, and
beginning with the most light-demanding, would run as
follows: Cottonwood, sycamore, red gum, white elm,
white ash, and red maple.

Demands upon Soil and Moisture

While the red gum grows in various situations, it prefers
the deep, rich soil of the hardwood bottoms, and there
reaches its best development (see Fig. 10). It requires
considerable soil moisture, though it does not grow
in the wetter swamps, and does not thrive on dry pine land.
Seedlings, however, are often found in large numbers on
the edges of the uplands and even on the sandy pine land,
but they seldom live beyond the pole stage. When they[57]
do, they form small, scrubby trees that are of little value.
Where the soil is dry the tree has a long tap root. In the
swamps, where the roots can obtain water easily, the development
of the tap root is poor, and it is only moderate
on the glade bottom lands, where there is considerable
moisture throughout the year, but no standing water in
the summer months.

Reproduction of Red Gum

Red gum reproduces both by seed and by sprouts
(see Fig. 12). It produces seed fairly abundantly every
year, but about once in three years there is an extremely
heavy production. The tree begins to bear seed when
twenty-five to thirty years old, and seeds vigorously up
to an age of one hundred and fifty years, when its productive
power begins to diminish. A great part of the
seed, however, is abortive. Red gum is not fastidious in
regard to its germinating bed; it comes up readily on sod[58]
in old fields and meadows, on decomposing humus in the
forest, or on bare clay-loam or loamy sand soil. It requires
a considerable degree of light, however, and prefers
a moist seed bed. The natural distribution of the seed
takes place for several hundred feet from the seed trees,
the dissemination depending almost entirely on the wind.
A great part of the seed falls on the hardwood bottom when
the land is flooded, and is either washed away or, if already[59]
in the ground and germinating, is destroyed by the long-continued
overflow. After germinating, the red gum
seedling demands, above everything else, abundant light
for its survival and development. It is for this reason
that there is very little growth of red gum, either in the
unculled forest or on culled land, where, as is usually the
case, a dense undergrowth of cane, briers, and rattan is
present. Under the dense underbrush of cane and briers
throughout much of the virgin forest, reproduction of any
of the merchantable species is of course impossible. And
even where the land has been logged over, the forest is
seldom open enough to allow reproduction of cottonwood
and red gum. Where, however, seed trees are contiguous
to pastures or cleared land, scattered seedlings are found
springing up in the open, and where openings occur in the
forest, there are often large numbers of red gum seedlings,
the reproduction generally occurring in groups. But over
the greater part of the Southern hardwood bottom land
forest reproduction is very poor. The growth of red gum
during the early part of its life, and up to the time it
reaches a diameter of eight inches breast-high, is extremely
rapid, and, like most of the intolerant species, it attains
its height growth at an early period. Gum sprouts readily
from the stump, and the sprouts surpass the seedlings in
rate of height growth for the first few years, but they seldom
form large timber trees. Those over fifty years of
age seldom sprout. For this reason sprout reproduction
is of little importance in the forest. The principal requirements
of red gum, then, are a moist, fairly rich soil
and good exposure to light. Without these it will not
reach its best development.

Second-Growth Red Gum

Second-growth red gum occurs to any considerable extent
only on land which has been thoroughly cleared.
Throughout the South there is a great deal of land which
was in cultivation before the Civil War, but which during
the subsequent period of industrial depression was abandoned
and allowed to revert to forest. These old fields
now mostly covered with second-growth forest, of[60]
which red gum forms an important part (see Fig. 12).
Frequently over fifty per cent of the stand consists of this
species, but more often, and especially on the Atlantic
coast, the greater part is of cottonwood or ash. These
stands are very dense, and the growth is extremely rapid.
Small stands of young growth are also often found along
the edges of cultivated fields. In the Mississippi Valley
the abandoned fields on which young stands have sprung
up are for the most part being rapidly cleared again. The
second growth here is considered of little value in comparison
with the value of the land for agricultural purposes.
In many cases, however, the farm value of the land is not
at present sufficient to make it profitable to clear it, unless
the timber cut will at least pay for the operation. There
is considerable land upon which the second growth will
become valuable timber within a few years. Such land
should not be cleared until it is possible to utilize the
timber.

39. Tupelo Gum (Nyssa aquatica) (Bay Poplar, Swamp
Poplar, Cotton Gum, Hazel Pine, Circassian Walnut,
Pepperidge, Nyssa). The close similarity which exists
between red and tupelo gum, together with the
fact that tupelo is often cut along with red gum, and
marketed with the sapwood of the latter, makes it
not out of place to give consideration to this timber.
The wood has a fine, uniform texture, is moderately
hard and strong, is stiff, not elastic, very tough and
hard to split, but easy to work with tools. Tupelo
takes glue, paint, or varnish well, and absorbs very
little of the material. In this respect it is equal to
yellow poplar and superior to cottonwood. The
wood is not durable in contact with ground, and requires
much care in seasoning. The distinction between
the heartwood and sapwood of this species is
marked. The former varies in color from a dull gray
to a dull brown; the latter is whitish or light yellow
like that of poplar. The wood is of medium weight,
about thirty-two pounds per cubic foot when dry, or
nearly that of red gum and loblolly pine. After[61]
seasoning it is difficult to distinguish the better grades
of sapwood from poplar. Owing to the prejudice
against tupelo gum, it was until recently marketed
under such names as bay poplar, swamp poplar, nyssa,
cotton gum, circassian walnut, and hazel pine. Since
it has become evident that the properties of the wood
fit it for many uses, the demand for tupelo has largely
increased, and it is now taking rank with other standard
woods under its rightful name. Heretofore the
quality and usefulness of this wood were greatly
underestimated, and the difficulty of handling it was
magnified. Poor success in seasoning and kiln-drying
was laid to defects of the wood itself, when, as a
matter of fact, the failures were largely due to the
absence of proper methods in handling. The passing
of this prejudice against tupelo is due to a better
understanding of the characteristics and uses of the
wood. Handled in the way in which its particular
character demands, tupelo is a wood of much value.

Uses of Tupelo Gum

Tupelo gum is now used in slack cooperage, principally
for heading. It is used extensively for house flooring and
inside finishing, such as mouldings, door jambs, and casings.
A great deal is now shipped to European countries, where
it is highly valued for different classes of manufacture.
Much of the wood is used in the manufacture of boxes, since
it works well upon rotary veneer machines. There is also
an increasing demand for tupelo for laths, wooden pumps,
violin and organ sounding boards, coffins, mantelwork,
conduits and novelties. It is also used in the furniture
trade for backing, drawers, and panels.

Range of Tupelo Gum

Tupelo occurs throughout the coastal region of the Atlantic
States, from southern Virginia to northern Florida,
through the Gulf States to the valley of the Nueces River
in Texas, through Arkansas and southern Missouri to
western Kentucky and Tennessee, and to the valley of[62]
the lower Wabash River. Tupelo is being extensively
milled at present only in the region adjacent to Mobile
Ala., and in southern and central Louisiana, where it
occurs in large merchantable quantities, attaining its
best development in the former locality. The country
in this locality is very swampy (see Fig. 11), and within
a radius of one hundred miles tupelo gum is one of the
principal timber trees. It grows only in the swamps and
wetter situations (see Fig. 11), often in mixture with
cypress, and in the rainy season it stands in from two to
twenty feet of water.

40. Black Gum (Nyssa sylvatica) (Sour Gum). Black
gum is not cut to much extent, owing to its less abundant
supply and poorer quality, but is used for repair
work on wagons, for boxes, crates, wagon hubs,
rollers, bowls, woodenware, and for cattle yokes and
other purposes which require a strong, non-splitting
wood. Heartwood is light brown in color, often
nearly white; sapwood hardly distinguishable, fine
grain, fibres interwoven. Wood is heavy, not hard,
difficult to work, strong, very tough, checks and
warps considerably in drying, not durable. It is
distributed from Maine to southern Ontario, through
central Michigan to southeastern Missouri, southward
to the valley of the Brazos River in Texas, and
eastward to the Kissimmee River and Tampa Bay
in Florida. It is found in the swamps and hardwood
bottoms, but is more abundant and of better size on the
slightly higher ridges and hummocks in these swamps,
and on the mountain slopes in the southern Alleghany
region. Though its range is greater than that of
either red or tupelo gum, it nowhere forms an important
part of the forest.

HACKBERRY

41. Hackberry (Celtis occidentalis) (Sugar Berry, Nettle
Tree). The wood is handsome, heavy, hard, strong,
quite tough, of moderately fine texture, and greenish
or yellowish color, shrinks moderately, works well[63]
and stands well, and takes a good polish. Used to
some extent in cooperage, and in the manufacture of
cheap furniture. Medium- to large-sized tree, locally
quite common, largest in the lower Mississippi Valley.
Occurs in nearly all parts of the eastern United States.

HICKORY

The hickories of commerce are exclusively North American
and some of them are large and beautiful trees of
60 to 70 feet or more in height. They are closely allied
to the walnut, and the wood is very like walnut in grain
and color, though of a somewhat darker brown. It is one
of the finest of American hardwoods in point of strength;
in toughness it is superior to ash, rather coarse in texture,
smooth and of straight grain, very heavy and strong as
well as elastic and tenacious, but decays rapidly, especially
the sapwood when exposed to damp and moisture, and
is very liable to attack from worms and boring insects.
The cross-section of hickory is peculiar, the annual rings
appear like fine lines instead of like the usual pores, and
the medullary rays, which are also very fine but distinct,
in crossing these form a peculiar web-like pattern which
is one of the characteristic differences between hickory
and ash. Hickory is rarely subjected to artificial treatment,
but there is this curious fact in connection with the
wood, that, contrary to most other woods, creosote is
only with difficulty injected into the sap, although there
is no difficulty in getting it into the heartwood. It dries
slowly, shrinks and checks considerably in seasoning; is not
durable in contact with the soil or if exposed. Hickory
excels as wagon and carriage stock, for hoops in cooperage,
and is extensively used in the manufacture of implements
and machinery, for tool handles, timber pins,
harness work, dowel pins, golf clubs, and fishing rods.
The hickories are tall trees with slender stems, never forming
forests, occasionally small groves, but usually occur
scattered among other broad-leaved trees in suitable localities.
The following species all contribute more or less
to the hickory of the markets:[64]

42. Shagbark Hickory (Hicoria ovata) (Shellbark Hickory,
Scalybark Hickory). A medium- to large-sized
tree, quite common; the favorite among the hickories.
Heartwood light brown, sapwood ivory or cream-colored.
Wood close-grained, compact structure,
annual rings clearly marked. Very hard, heavy,
strong, tough, and flexible, but not durable in contact
with the soil or when exposed. Used for agricultural
implements, wheel runners, tool handles,
vehicle parts, baskets, dowel pins, harness work, golf
clubs, fishing rods, etc. Best developed in the Ohio
and Mississippi basins; from Lake Ontario to Texas,
Minnesota to Florida.

43. Mockernut Hickory (Hicoria alba) (Black Nut Hickory,
Black Hickory, Bull Nut Hickory, Big Bud
Hickory, White Heart Hickory). A medium- to large-sized
tree. Wood in its quality and uses similar to
the preceding. Its range is the same as that of
Hicoria ovata. Common, especially in the South.

44. Pignut Hickory (Hicoria glabra) (Brown Hickory,
Black Hickory, Switchbud Hickory). A medium- to
large-sized tree. Heavier and stronger than any
of the preceding. Heartwood light to dark brown,
sapwood nearly white. Abundant, all eastern United
States.

45. Bitternut Hickory (Hicoria minima) (Swamp Hickory).
A medium-sized tree, favoring wet localities.
Heartwood light brown, sapwood lighter color. Wood
in its quality and uses not so valuable as Hicoria
ovata, but is used for the same purposes. Abundant,
all eastern United States.

46. Pecan (Hicoria pecan) (Illinois Nut). A large tree,
very common in the fertile bottoms of the western
streams. Indiana to Nebraska and southward to
Louisiana and Texas.

HOLLY

47. Holly (Ilex opaca). Small to medium-sized tree.
Wood of medium weight, hard, strong, tough, of[65]
exceedingly fine grain, closer in texture than most
woods, of white color, sometimes almost as white as
ivory; requires great care in its treatment to preserve
the whiteness of the wood. It does not readily
absorb foreign matter. Much used by turners and
for all parts of musical instruments, for handles on
whips and fancy articles, draught-boards, engraving
blocks, cabinet work, etc. The wood is often dyed
black and sold as ebony; works well and stands well.
Most abundant in the lower Mississippi Valley and
Gulf States, but occurring eastward to Massachusetts
and north to Indiana.

48. Holly (Ilex monticolo) (Mountain Holly). Small-sized
tree. Wood in its quality and uses similar to
the preceding, but is not very generally known. It
is found in the Catskill Mountains and extends southward
along the Alleghanies as far as Alabama.

HORSE CHESTNUT (See Buckeye)

IRONWOOD

49. Ironwood (Ostrya Virginiana) (Hop Hornbeam, Lever
Wood). Small-sized tree, common. Heartwood light
brown tinged with red, sapwood nearly white. Wood
heavy, tough, exceedingly close-grained, very strong
and hard, durable in contact with the soil, and will
take a fine polish. Used for small articles like levers,
handles of tools, mallets, etc. Ranges throughout
the United States east of the Rocky Mountains.

LAUREL

50. Laurel (Umbellularia Californica) (Myrtle). A Western
tree, produces timber of light brown color of great
size and beauty, and is very valuable for cabinet and
inside work, as it takes a fine polish. California and
Oregon, coast range of the Sierra Nevada Mountains.[66]

LOCUST

51. Black Locust (Robinia pseudacacia) (Locust, Yellow
Locust, Acacia). Small to medium-sized tree. Wood
very heavy, hard, strong, and tough, rivalling some
of the best oak in this latter quality. The wood has
great torsional strength, excelling most of the soft
woods in this respect, of coarse texture, close-grained
and compact structure, takes a fine polish. Annual
rings clearly marked, very durable in contact with
the soil, shrinks and checks considerably in drying,
the very narrow sapwood greenish yellow, the heartwood brown,
with shades of red and green. Used
for wagon hubs, trenails or pins, but especially for
railway ties, fence posts, and door sills. Also used
for boat parts, turnery, ornamentations, and locally
for construction. Abroad it is much used for furniture
and farming implements and also in turnery. At
home in the Alleghany Mountains, extensively planted,
especially in the West.

52. Honey Locust (Gleditschia triacanthos) (Honey Shucks,
Locust, Black Locust, Brown Locust, Sweet Locust,
False Acacia, Three-Thorned Acacia). A medium-sized
tree. Wood heavy, hard, strong, tough, durable
in contact with the soil, of coarse texture, susceptible
to a good polish. The narrow sapwood yellow,
the heartwood brownish red. So far, but little appreciated
except for fences and fuel. Used to some
extent for wheel hubs, and locally in rough construction.
Found from Pennsylvania to Nebraska,
and southward to Florida and Texas; locally quite
abundant.

53. Locust (Robinia viscosa) (Clammy Locust). Usually
a shrub five or six feet high, but known to reach a
height of 40 feet in the mountains of North Carolina,
with the habit of a tree. Wood light brown, heavy,
hard, and close-grained. Not used to much extent
in manufacture. Range same as the preceding.[67]

MAGNOLIA

54. Magnolia (Magnolia glauca) (Swamp Magnolia, Small
Magnolia, Sweet Bay, Beaver Wood). Small-sized
tree. Heartwood reddish brown, sap wood cream
white. Sparingly used in manufacture. Ranges from
Essex County, Mass., to Long Island, N. Y., from
New Jersey to Florida, and west in the Gulf region
to Texas.

55. Magnolia (Magnolia tripetala) (Umbrella Tree). A
small-sized tree. Wood in its quality similiar to the
preceding. It may be easily recognized by its great
leaves, twelve to eighteen inches long, and five to
eight inches broad. This species as well as the preceding
is an ornamental tree. Ranges from Pennsylvania
southward to the Gulf.

56. Cucumber Tree (Magnolia accuminata) (Tulip-wood,
Poplar). Medium- to large-sized tree. Heartwood
yellowish brown, sapwood almost white. Wood light,
soft, satiny, close-grained, durable in contact with
the soil, resembling and sometimes confounded with
tulip tree (Liriodendron tulipifera) in the markets.
The wood shrinks considerably, but seasons without
much injury, and works and stands well. It bends
readily when steamed, and takes stain and paint well.
Used in cooperage, for siding, for panelling and finishing
lumber in house, car and shipbuilding, etc., also
in the manufacture of toys, culinary woodenware, and
backing for drawers. Most common in the southern
Alleghanies, but distributed from western New York
to southern Illinois, south through central Kentucky
and Tennessee to Alabama, and throughout
Arkansas.

MAPLE

Wood heavy, hard, strong, stiff, and tough, of fine
texture, frequently wavy-grained, this giving rise to
“curly” and “blister” figures which are much admired.
Not durable in the ground, or when exposed. Maple[68]
is creamy white, with shades of light brown in the heartwood,
shrinks moderately, seasons, works, and stands well,
wears smoothly, and takes a fine polish. The wood is
used in cooperage, and for ceiling, flooring, panelling,
stairway, and other finishing lumber in house, ship, and
car construction. It is used for the keels of boats and ships,
in the manufacture of implements and machinery, but
especially for furniture, where entire chamber sets of
maple rival those of oak. Maple is also used for shoe
lasts and other form blocks; for shoe pegs; for piano
actions, school apparatus, for wood type in show bill
printing, tool handles, in wood carving, turnery, and
scroll work, in fact it is one of our most useful woods.
The maples are medium-sized trees, of fairly rapid growth,
sometimes form forests, and frequently constitute a large
proportion of the arborescent growth. They grow freely
in parts of the Northern Hemisphere, and are particularly
luxuriant in Canada and the northern portions of the
United States.

57. Sugar Maple (Acer saccharum) (Hard Maple, Rock
Maple). Medium- to large-sized tree, very common,
forms considerable forests, and is especially esteemed.
The wood is close-grained, heavy, fairly hard and
strong, of compact structure. Heartwood brownish,
sapwood lighter color; it can be worked to a satin-like
surface and take a fine polish, it is not durable
if exposed, and requires a good deal of seasoning.
Medullary rays small but distinct. The “curly”
or “wavy” varieties furnish wood of much beauty,
the peculiar contortions of the grain called “bird’s
eye” being much sought after, and used as veneer for
panelling, etc. It is used in all good grades of furniture,
cabinetmaking, panelling, interior finish, and
turnery; it is not liable to warp and twist. It is also
largely used for flooring, for rollers for wringers and
mangling machines, for which there is a large and
increasing demand. The peculiarity known as “bird’s
eye,” and which causes a difficulty in working the
wood smooth, owing to the little pieces like knots[69]
lifting up, is supposed to be due to the action of boring
insects. Its resistance to compression across the
grain is higher than that of most other woods. Ranges
from Maine to Minnesota, abundant, with birch, in
the region of the Great Lakes.

58. Red Maple (Acer rubrum) (Swamp Maple, Soft
Maple, Water Maple). Medium-sized tree. Like
the preceding but not so valuable. Scattered along
water-courses and other moist localities. Abundant.
Maine to Minnesota, southward to northern Florida.

59. Silver Maple (Acer saccharinum) (Soft Maple, White
Maple, Silver-Leaved Maple). Medium- to large-sized
tree, common. Wood lighter, softer, and inferior
to Acer saccharum, and usually offered in small
quantities and held separate in the markets. Heartwood
reddish brown, sapwood ivory white, fine-grained,
compact structure. Fibres sometimes
twisted, weaved, or curly. Not durable. Used in
cooperage for woodenware, turnery articles, interior
decorations and flooring. Valley of the Ohio, but
occurs from Maine to Dakota and southward to
Florida.

60. Broad-Leaved Maple (Acer macrophyllum) (Oregon
Maple). Medium-sized tree, forms considerable
forests, and, like the preceding has a lighter, softer,
and less valuable wood than Acer saccharum. Pacific
Coast regions.

61. Mountain Maple (Acer spicatum). Small-sized tree.
Heartwood pale reddish brown, sapwood lighter color.
Wood light, soft, close-grained, and susceptible of
high polish. Ranges from lower St. Lawrence River
to northern Minnesota and regions of the Saskatchewan
River; south through the Northern States and
along the Appalachian Mountains to Georgia.

62. Ash-Leaved Maple (Acer negundo) (Box Elder).
Medium- to large-sized tree. Heartwood creamy
white, sapwood nearly white. Wood light, soft, close-grained,[70]
not strong. Used for woodenware and paper
pulp. Distributed across the continent, abundant
throughout the Mississippi Valley along banks of
streams and borders of swamps.

63. Striped Maple (Acer Pennsylvanicum) (Moose-wood).
Small-sized tree. Produces a very white wood much
sought after for inlaid and for cabinet work. Wood
is light, soft, close-grained, and takes a fine polish.
Not common. Occurs from Pennsylvania to Minnesota.

MULBERRY

64. Red Mulberry (Morus rubra). A small-sized tree.
Wood moderately heavy, fairly hard and strong,
rather tough, of coarse texture, very durable in contact
with the soil. The sapwood whitish, heartwood
yellow to orange brown, shrinks and checks considerably
in drying, works well and stands well. Used
in cooperage and locally in construction, and in the
manufacture of farm implements. Common in the
Ohio and Mississippi Valleys, but widely distributed
in the eastern United States.

MYRTLE (See Laurel)

OAK

Wood very variable, usually very heavy and hard, very
strong and tough, porous, and of coarse texture. The
sapwood whitish, the heartwood “oak” to reddish brown.
It shrinks and checks badly, giving trouble in seasoning,
but stands well, is durable, and little subject to the attacks
of boring insects. Oak is used for many purposes,
and is the chief wood used for tight cooperage; it is used
in shipbuilding, for heavy construction, in carpentry, in
furniture, car and wagon work, turnery, and even in woodcarving.
It is also used in all kinds of farm implements,
mill machinery, for piles and wharves, railway ties, etc.,
etc. The oaks are medium- to large-sized trees, forming
the predominant part of a large proportion of our broad-leaved[71]
forests, so that these are generally termed “oak
forests,” though they always contain considerable proportion
of other kinds of trees. Three well-marked kinds—white,
red, and live oak—are distinguished and kept
separate in the markets. Of the two principal kinds
“white oak” is the stronger, tougher, less porous, and
more durable. “Red oak” is usually of coarser texture,
more porous, often brittle, less durable, and even more
troublesome in seasoning than white oak. In carpentry
and furniture work red oak brings the same price at present
as white oak. The red oaks everywhere accompany the
white oaks, and, like the latter, are usually represented
by several species in any given locality. “Live oak,”
once largely employed in shipbuilding, possesses all the
good qualities, except that of size, of white oak, even to
a greater degree. It is one of the heaviest, hardest, toughest,
and most durable woods of this country. In structure
it resembles the red oak, but is less porous.

65. White Oak (Quercus alba) (American Oak). Medium-
to large-sized tree. Heartwood light brown,
sapwood lighter color. Annual rings well marked,
medullary rays broad and prominent. Wood tough,
strong, heavy, hard, liable to check in seasoning,
durable in contact with the soil, takes a high polish,
very elastic, does not shrink much, and can be bent
to any form when steamed. Used for agricultural
implements, tool handles, furniture, fixtures, interior
finish, car and wagon construction, beams,
cabinet work, tight cooperage, railway ties, etc., etc.
Because of the broad medullary rays, it is generally
“quarter-sawn” for cabinet work and furniture.
Common in the Eastern States, Ohio and Mississippi
Valleys. Occurs throughout the eastern United
States.

66. White Oak (Quercus durandii). Medium- to small-sized
tree. Wood in its quality and uses similiar to
the preceding. Texas, eastward to Alabama.

67. White Oak (Quercus garryana) (Western White Oak).
Medium- to large-sized tree. Stronger, more durable,[72]
and wood more compact than Quercus alba. Washington
to California.

68. White Oak (Quercus lobata). Medium- to large-sized
tree. Largest oak on the Pacific Coast. Wood in
its quality and uses similar to Quercus alba, only it
is finer-grained. California.

69. Bur Oak (Quercus macrocarpa) (Mossy-Cup Oak,
Over-Cup Oak). Large-sized tree. Heartwood “oak”
brown, sapwood lighter color. Wood heavy, strong,
close-grained, durable in contact with the soil.
Used in ship- and boatbuilding, all sorts of construction,
interior finish of houses, cabinet work,
tight cooperage, carriage and wagon work, agricultural
implements, railway ties, etc., etc. One of the most
valuable and most widely distributed of American
oaks, 60 to 80 feet in height, and, unlike most of the
other oaks, adapts itself to varying climatic conditions.
It is one of the most durable woods when in
contact with the soil. Common, locally abundant.
Ranges from Manitoba to Texas, and from the foot
hills of the Rocky Mountains to the Atlantic Coast.
It is the most abundant oak of Kansas and Nebraska,
and forms the scattered forests known as “The oak
openings” of Minnesota.

70. Willow Oak (Quercus phellos) (Peach oak). Small
to medium-sized tree. Heartwood pale reddish brown,
sapwood lighter color. Wood heavy, hard, strong,
coarse-grained. Occasionally used in construction.
New York to Texas, and northward to Kentucky.

71. Swamp White Oak (Quercus bicolor var. platanoides).
Large-sized tree. Heartwood pale brown, sapwood
the same color. Wood heavy, hard, strong, tough,
coarse-grained, checks considerably in seasoning.
Used in construction, interior finish of houses, carriage-
and boatbuilding, agricultural implements, in cooperage,
railway ties, fencing, etc., etc. Ranges from
Quebec to Georgia and westward to Arkansas. Never
abundant. Most abundant in the Lake States.[73]

72. Over-Cup Oak (Quercus lyrata) (Swamp White Oak,
Swamp Post Oak). Medium to large-sized tree,
rather restricted, as it grows in the swampy districts
of Carolina and Georgia. Is a larger tree than most
of the other oaks, and produces an excellent timber,
but grows in districts difficult of access, and is not
much used. Lower Mississippi and eastward to
Delaware.

73. Pin Oak (Quercus palustris) (Swamp Spanish Oak,
Water Oak). Medium- to large-sized tree. Heartwood
pale brown with dark-colored sap wood. Wood
heavy, strong, and coarse-grained. Common along
the borders of streams and swamps, attains its greatest
size in the valley of the Ohio. Arkansas to Wisconsin,
and eastward to the Alleghanies.

74. Water Oak (Quercus aquatica) (Duck Oak, Possum
Oak). Medium- to large-sized tree, of extremely
rapid growth. Eastern Gulf States, eastward to
Delaware and northward to Missouri and Kentucky.

75. Chestnut Oak (Quercus prinus) (Yellow Oak, Rock
Oak, Rock Chestnut Oak). Heartwood dark brown,
sapwood lighter color. Wood heavy, hard, strong,
tough, close-grained, durable in contact with the soil.
Used for railway ties, fencing, fuel, and locally for
construction. Ranges from Maine to Georgia and
Alabama, westward through Ohio, and southward
to Kentucky and Tennessee.

76. Yellow Oak (Quercus acuminata) (Chestnut Oak,
Chinquapin Oak). Medium- to large-sized tree.
Heartwood dark brown, sapwood pale brown. Wood
heavy, hard, strong, close-grained, durable in contact
with the soil. Used in the manufacture of wheel
stock, in cooperage, for railway ties, fencing, etc.,
etc. Ranges from New York to Nebraska and eastern
Kansas, southward in the Atlantic region to the
District of Columbia, and west of the Alleghanies
southward to the Gulf States.[74]

77. Chinquapin Oak (Quercus prinoides) (Dwarf Chinquapin
Oak, Scrub Chestnut Oak). Small-sized tree.
Heartwood light brown, sapwood darker color. Does
not enter the markets to any great extent. Ranges
from Massachusetts to North Carolina, westward to
Missouri, Nebraska, Kansas, and eastern Texas.
Reaches its best form in Missouri and Kansas.

78. Basket Oak (Quercus michauxii) (Cow Oak). Large-sized
tree. Locally abundant. Lower Mississippi
and eastward to Delaware.

79. Scrub Oak (Quercus ilicifolia var. pumila) (Bear Oak).
Small-sized tree. Heartwood light brown, sapwood
darker color. Wood heavy, hard, strong, and coarse-grained.
Found in New England and along the
Alleghanies.

80. Post Oak (Quercus obtusiloda var. minor) (Iron Oak).
Medium- to large-sized tree, gives timber of great
strength. The color is of a brownish yellow hue,
close-grained, and often superior to the white oak
(Quercus alba) in strength and durability. It is used
for posts and fencing, and locally for construction.
Arkansas to Texas, eastward to New England and
northward to Michigan.

81. Red Oak (Quercus rubra) (Black Oak). Medium- to
large-sized tree. Heartwood light brown to red, sapwood
lighter color. Wood coarse-grained, well-marked
annual rings, medullary rays few but broad. Wood
heavy, hard, strong, liable to check in seasoning.
It is found over the same range as white oak, and
is more plentiful. Wood is spongy in grain, moderately
durable, but unfit for work requiring strength.
Used for agricultural implements, furniture, bob
sleds, vehicle parts, boxes, cooperage, woodenware,
fixtures, interior finish, railway ties, etc., etc. Common
in all parts of its range. Maine to Minnesota,
and southward to the Gulf.

82. Black Oak (Quercus tinctoria var. velutina) (Yellow
Oak). Medium- to large-sized tree. Heartwood[75]
bright brown tinged with red, sapwood lighter color.
Wood heavy, hard, strong, coarse-grained, checks
considerably in seasoning. Very common in the
Southern States, but occurring North as far as Minnesota,
and eastward to Maine.

83. Barren Oak (Quercus nigra var. marilandica) (Black
Jack, Jack Oak). Small-sized tree. Heartwood
dark brown, sapwood lighter color. Wood heavy,
hard, strong, coarse-grained, not valuable. Used
in the manufacture of charcoal and for fuel. New
York to Kansas and Nebraska, and southward to
Florida. Rare in the North, but abundant in the
South.

84. Shingle Oak (Quercus imbricaria) (Laurel Oak). Small
to medium-sized tree. Heartwood pale reddish
brown, sapwood lighter color. Wood heavy, hard,
strong, coarse-grained, checks considerably in drying.
Used for shingles and locally for construction.
Rare in the east, most abundant in the lower Ohio
Valley. From New York to Illinois and southward.
Reaches its greatest size in southern Illinois and
Indiana.

85. Spanish Oak (Quercus digitata var. falcata) (Red Oak).
Medium-sized tree. Heartwood light reddish brown,
sapwood much lighter. Wood heavy, hard, strong,
coarse-grained, and checks considerably in seasoning.
Used locally for construction, and has high fuel value.
Common in south Atlantic and Gulf region, but found
from Texas to New York, and northward to Missouri
and Kentucky.

86. Scarlet Oak (Quercus coccinea). Medium- to large-sized
tree. Heartwood light reddish-brown, sapwood
darker color. Wood heavy, hard, strong, and
coarse-grained. Best developed in the lower basin
of the Ohio, but found from Minnesota to Florida.

87. Live Oak (Quercus virens) (Maul Oak). Medium- to
large-sized tree. Grows from Maryland to the Gulf[76]
of Mexico, and often attains a height of 60 feet and
4 feet in diameter. The wood is hard, strong, and
durable, but of rather rapid growth, therefore not
as good quality as Quercus alba. The live oak of
Florida is now reserved by the United States Government
for Naval purposes. Used for mauls and mallets,
tool handles, etc., and locally for construction.
Scattered along the coast from Maryland to Texas.

88. Live Oak (Quercus chrysolepis) (Maul Oak, Valparaiso
Oak). Medium- to small-sized tree. California.

OSAGE ORANGE

89. Osage Orange (Maclura aurantiaca) (Bois d’Arc).
A small-sized tree of fairly rapid growth. Wood
very heavy, exceedingly hard, strong, not tough, of
moderately coarse texture, and very durable and
elastic. Sapwood yellow, heartwood brown on the
end face, yellow on the longitudinal faces, soon
turning grayish brown if exposed. It shrinks considerably
in drying, but once dry it stands unusually
well. Much used for wheel stock, and wagon framing;
it is easily split, so is unfit for wheel hubs, but is very
suitable for wheel spokes. It is considered one of
the timbers likely to supply the place of black locust
for insulator pins on telegraph poles. Seems too
little appreciated; it is well suited for turned ware
and especially for woodcarving. Used for spokes,
insulator pins, posts, railway ties, wagon framing,
turnery, and woodcarving. Scattered through the
rich bottoms of Arkansas and Texas.

PAPAW

90. Papaw (Asimina triloba) (Custard Apple). Small-sized
tree, often only a shrub, Heartwood pale,
yellowish green, sapwood lighter color. Wood light,
soft, coarse-grained, and spongy. Not used to any
extent in manufacture. Occurs in eastern and central
Pennsylvania, west as far as Michigan and Kansas,
and south to Florida and Texas. Often forming[77]
dense thickets in the lowlands bordering the Mississippi
River.

PERSIMMON

91. Persimmon (Diospyros Virginiana). Small to medium-sized
tree. Wood very heavy, and hard, strong and
tough; resembles hickory, but is of finer texture and
elastic, but liable to split in working. The broad
sapwood cream color, the heartwood brown, sometimes
almost black. The persimmon is the Virginia
date plum, a tree of 30 to 50 feet high, and 18 to 20
inches in diameter; it is noted chiefly for its fruit,
but it produces a wood of considerable value. Used
in turnery, for wood engraving, shuttles, bobbins,
plane stock, shoe lasts, and largely as a substitute
for box (Buxus sempervirens)—especially the black
or Mexican variety,—also used for pocket rules and
drawing scales, for flutes and other wind instruments.
Common, and best developed in the lower
Ohio Valley, but occurs from New York to Texas
and Missouri.

POPLAR (See also Tulip Wood)

Wood light, very soft, not strong, of fine texture, and
whitish, grayish to yellowish color, usually with a satiny
luster. The wood shrinks moderately (some cross-grained
forms warp excessively), but checks very little in seasoning;
is easily worked, but is not durable. Used in cooperage,
for building and furniture lumber, for crates and
boxes (especially cracker boxes), for woodenware, and
paper pulp.

92. Cottonwood (Populus monilifera, var. angulata) (Carolina
Poplar). Large-sized tree, forms considerable
forests along many of the Western streams, and
furnishes most of the cottonwood of the market.
Heartwood dark brown, sapwood nearly white. Wood
light, soft, not strong, and close-grained (see Fig.
14). Mississippi Valley and West. New England
to the Rocky Mountains.[78]

93. Cottonwood (Populus fremontii var. wislizeni). Medium-
to large-sized tree. Common. Wood in its
quality and uses similiar to the preceding, but not
so valuable. Texas to California.

94. Black Cottonwood (Populus trichocarpa var. heterophylla)
(Swamp Cottonwood, Downy Poplar). The
largest deciduous tree of Washington. Very common.[79]
Heartwood dull brown, sapwood lighter brown. Wood
soft, close-grained. Is now manufactured into lumber
in the West and South, and used in interior finish
of buildings. Northern Rocky Mountains and
Pacific region.

95. Poplar (Populus grandidentata) (Large-Toothed Aspen).
Medium-sized tree. Heartwood light brown,
sapwood nearly white. Wood soft and close-grained,
neither strong nor durable. Chiefly used for wood
pulp. Maine to Minnesota and southward along
the Alleghanies.

96. White Poplar (Populus alba) (Abele-Tree). Small
to medium-sized tree. Wood in its quality and uses
similar to the preceding. Found principally along
banks of streams, never forming forests. Widely
distributed in the United States.

97. Lombardy Poplar (Populus nigra italica). Medium-
to large-sized tree. This species is the first ornamental
tree introduced into the United States, and
originated in Afghanistan. Does not enter into the
markets. Widely planted in the United States.

98. Balsam (Populus balsamifera) (Balm of Gilead, Tacmahac).
Medium- to large-sized tree. Heartwood light
brown, sapwood nearly white. Wood light, soft,
not strong, close-grained. Used extensively in the
manufacture of paper pulp. Common all along the
northern boundary of the United States.

99. Aspen (Populus tremuloides) (Quaking Aspen). Small
to medium-sized tree, often forming extensive forests,
and covering burned areas. Heartwood light brown,
sapwood nearly white. Wood light, soft, close-grained,
neither strong nor durable. Chiefly used
for woodenware, cooperage, and paper pulp. Maine
to Washington and northward, and south in the
western mountains to California and New Mexico.

RED GUM (See Gum)[80]

SASSAFRAS

100. Sassafras (Sassafras sassafras). Medium-sized tree,
largest in the lower Mississippi Valley. Wood light,
soft, not strong, brittle, of coarse texture, durable
in contact with the soil. The sapwood yellow, the
heartwood orange brown. Used to some extent in
slack cooperage, for skiff- and boatbuilding, fencing,
posts, sills, etc. Occurs from New England to Texas
and from Michigan to Florida.

SOUR GUM (See Gum)

SOURWOOD

101. Sourwood (Oxydendrum arboreum) (Sorrel-Tree). A
slender tree, reaching the maximum height of 60 feet.
Heartwood reddish brown, sapwood lighter color.
Wood heavy, hard, strong, close-grained, and takes
a fine polish. Ranges from Pennsylvania, along the
Alleghanies, to Florida and Alabama, westward through
Ohio to southern Indiana and southward through
Arkansas and Louisiana to the Coast.

SWEET GUM (See Gum)

SYCAMORE

102. Sycamore (Platanus occidentalis) (Buttonwood, Button-Ball
Tree, Plane Tree, Water Beech). A large-sized
tree, of rapid growth. One of the largest deciduous
trees of the United States, sometimes attaining a
height of 100 feet. It produces a timber that is moderately
heavy, quite hard, stiff, strong, and tough,
usually cross-grained; of coarse texture, difficult to
split and work, shrinks moderately, but warps and
checks considerably in seasoning, but stands well,
and is not considered durable for outside work, or in
contact with the soil. It has broad medullary rays,
and much of the timber has a beautiful figure. It
is used in slack cooperage, and quite extensively for[81]
drawers, backs, and bottoms, etc., in furniture work.
It is also used for cabinet work, for tobacco boxes,
crates, desks, flooring, furniture, ox-yokes, butcher
blocks, and also for finishing lumber, where it has too
long been underrated. Common and largest in the
Ohio and Mississippi Valleys, at home in nearly all
parts of the eastern United States.

103. Sycamore (Platanus racemosa). The California
species, resembling in its wood the Eastern form.
Not used to any great extent.

TULIP TREE

104. Tulip Tree (Liriodendron tulipifera) (Yellow Poplar,
Tulip Wood, White Wood, Canary Wood, Poplar,
Blue Poplar, White Poplar, Hickory Poplar). A
medium- to large-sized tree, does not form forests,
but is quite common, especially in the Ohio basin.
Wood usually light, but varies in weight, it is soft,
tough, but not strong, of fine texture, and yellowish
color. The wood shrinks considerably, but seasons
without much injury, and works and stands extremely
well. Heartwood light yellow or greenish brown,
the sapwood is thin, nearly white, and decays rapidly.
The heartwood is fairly durable when exposed to the
weather or in contact with the soil. It bends readily
when steamed, and takes stain and paint well. The
mature forest-grown tree has a long, straight, cylindrical
bole, clear of branches for at least two thirds of
its length, surmounted by a short, open, irregular
crown. When growing in the open, the tree maintains
a straight stem, but the crown extends almost
to the ground, and is of conical shape. Yellow poplar,
or tulip wood, ordinarily grows to a height of from
100 to 125 feet, with a diameter of from 3 to 6 feet,
and a clear length of about 70 feet. Trees have been
found 190 feet high and ten feet in diameter. Used
in cooperage, for siding, for panelling and finishing
lumber in houses, car- and shipbuilding, for sideboards,
panels of wagons and carriages, for aeroplanes,[82]
for automobiles, also in the manufacture of furniture
farm implements, machinery, for pump logs, and
almost every kind of common woodenware, boxes
shelving, drawers, etc., etc. Also in the manufacture
of toys, culinary woodenware, and backing for veneer.
It is in great demand throughout the vehicle and implement
trade, and also makes a fair grade of wood
pulp. In fact the tulip tree is one of the most useful
of woods throughout the woodworking industry
of this country. Occurs from New England to Missouri
and southward to Florida.

TUPELO (See Gum)

WAAHOO

105. Waahoo (Evonymus atropurpureus). (Burning Bush,
Spindle Tree). A small-sized tree. Wood white,
tinged with orange; heavy, hard, tough, and close-grained,
works well and stands well. Used principally
for arrows and spindles. Widely distributed.
Usually a shrub six to ten feet high, becoming a tree
only in southern Arkansas and Oklahoma.

WALNUT

106. Black Walnut (Juglans nigra) (Walnut). A large,
beautiful, and quickly-growing tree, about 60 feet and
upwards in height. Wood heavy, hard, strong, of
coarse texture, very durable in contact with the soil.
The narrow sapwood whitish, the heartwood dark,
rich, chocolate brown, sometimes almost black; aged
trees of fine quality bring fancy prices. The wood
shrinks moderately in seasoning, works well and stands
well, and takes a fine polish. It is quite handsome,
and has been for a long time the favorite wood for
cabinet and furniture making. It is used for gun-stocks,
fixtures, interior decoration, veneer, panelling,
stair newells, and all classes of work demanding
a high priced grade of wood. Black walnut is
a large tree with stout trunk, of rapid growth, and[83]
was formerly quite abundant throughout the Alleghany
region. Occurs from New England to Texas,
and from Michigan to Florida. Not common.

WHITE WALNUT (See Butternut)

WHITE WOOD (See Tulip and also Basswood)

WHITE WILLOW

107. White Willow (Salix alba var. vitellina) (Willow,
Yellow Willow, Blue Willow). The wood is very
soft, light, flexible, and fairly strong, is fairly durable
in contact with the soil, works well and stands well
when seasoned. Medium-sized tree, characterized
by a short, thick trunk, and a large, rather irregular
crown composed of many branches. The size of
the tree at maturity varies with the locality. In
the region where it occurs naturally, a height of 70
to 80 feet, and a diameter of three to four feet are
often attained. When planted in the Middle West,
a height of from 50 to 60 feet, and a diameter of one
and one-half to two feet are all that may be expected.
When closely planted on moist soil, the tree forms a
tall, slender stem, well cleared branches. Is widely
naturalized in the United States. It is used in cooperage,
for woodenware, for cricket and baseball bats,
for basket work, etc. Charcoal made from the wood
is used in the manufacture of gunpowder. It has
been generally used for fence posts on the Northwestern
plains, because of scarcity of better material.
Well seasoned posts will last from four to seven
years. Widely distributed throughout the United
States.

108. Black Willow (Salix nigra). Small-sized tree.
Heartwood light reddish brown, sapwood nearly
white. Wood soft, light, not strong, close-grained,
and very flexible. Used in basket making, etc.
Ranges from New York to Rocky Mountains and
southward to Mexico.[84]

109. Shining Willow (Salix lucida). A small-sized tree.
Wood in its quality and uses similiar to the preceding.
Ranges from Newfoundland to Rocky Mountains
and southward to Pennsylvania and Nebraska.

110. Perch Willow (Salix amygdaloides) (Almond-leaf
Willow). Small to medium-sized tree. Heartwood
light brown, sapwood lighter color. Wood light,
soft, flexible, not strong, close-grained. Uses similiar
to the preceding. Follows the water courses and
ranges across the continent; less abundant in New
England than elsewhere. Common in the West.

111. Long-Leaf Willow (Salix fluviatilis) (Sand Bar Willow).
A small-sized tree. Ranges from the Arctic
Circle to Northern Mexico.

112. Bebb Willow (Salix bebbiana var. rostrata). A small-sized
tree. More abundant in British America than
in the United States, where it ranges southward to
Pennsylvania and westward to Minnesota.

113. Glaucous Willow (Salix discolor) (Pussy Willow).
A small-sized tree. Common along the banks of
streams, and ranges from Nova Scotia to Manitoba,
and south to Delaware; west to Indiana and northwestern
Missouri.

114. Crack Willow (Salix fragilis). A medium to large-sized
tree. Wood is very soft, light, very flexible
and fairly strong, is fairly durable in contact with
the soil, works well and stands well. Used principally
for basket making, hoops, etc., and to produce
charcoal for gunpowder. Very common, and
widely distributed in the United States.

115. Weeping Willow (Salix babylonica). Medium- to
large-sized tree. Wood similiar to Salix nigra, but
not so valuable. Mostly an ornamental tree. Originally
came from China. Widely planted in the
United States.[85]

YELLOW WOOD

116. Yellow Wood (Cladrastis lutea) (Virgilia). A small
to medium-sized tree. Wood yellow to pale brown,
heavy, hard, close-grained and strong. Not used
to much extent in manufacturing. Not common.
Found principally on the limestone cliffs of Kentucky,
Tennessee, and North Carolina.

SECTION IV[86]

GRAIN, COLOR, ODOR, WEIGHT,
AND FIGURE IN WOOD

DIFFERENT GRAINS OF WOOD

The terms “fine-grained,” “coarse-grained,” “straight-grained,”
and “cross-grained” are frequently applied in
the trade. In common usage, wood is coarse-grained if
its annual rings are wide; fine-grained if they are narrow.
In the finer wood industries a fine-grained wood is capable
of high polish, while a coarse-grained wood is not, so
that in this latter case the distinction depends chiefly on
hardness, and in the former on an accidental case of slow
or rapid growth. Generally if the direction of the wood
fibres is parallel to the axis of the stem or limb in which
they occur, the wood is straight-grained; but in many
cases the course of the fibres is spiral or twisted around
the tree (as shown in Fig. 15), and sometimes commonly
in the butts of gum and cypress, the fibres of several layers
are oblique in one direction, and those of the next series
of layers are oblique in the opposite direction. (As shown
in Fig. 16 the wood is cross or twisted grain.) Wavy-grain
in a tangential plane as seen on the radial section is
illustrated in Fig. 17, which represents an extreme case
observed in beech. This same form also occurs on the
radial plane, causing the tangential section to appear wavy
or in transverse folds.

When wavy grain is fine (i.e., the folds or ridges small
but numerous) it gives rise to the “curly” structure
frequently seen in maple. Ordinarily, neither wavy,
spiral, nor alternate grain is visible on the cross-section;
its existence often escapes the eye even on smooth, longitudinal
faces in the sawed material, so that the only[87]
guide to their discovery lies in splitting the wood in two,
in the two normal plains.

Generally the surface of the wood under the bark, and
therefore also that of any layer in the interior, is not uniform
and smooth, but is channelled and pitted by numerous
depressions, which differ greatly in size and form.
Usually, any one depression or elevation is restricted to
one or few annual layers (i.e., seen only in one or few rings)
and is then lost, being compensated (the surface at the
particular spot evened up) by growth. In some woods,
however, any depression or elevation once attained grows
from year to year and reaches a maximum size, which is
maintained for many years, sometimes throughout life.
In maple, where this tendency to preserve any particular
contour is very great, the depressions and elevations are[88]
usually small (commonly less than one-eighth inch) but
very numerous.

On tangent boards of such wood, the sections, pits, and
prominences appear as circlets, and give rise to the beautiful
“bird’s eye” or “landscape” structure. Similiar structures
in the burls of black ash, maple, etc., are frequently
due to the presence of dormant buds, which cause the
surface of all the layers through which they pass to be
covered by small conical elevations, whose cross-sections
on the sawed board appear as irregular circlets or islets,
each with a dark speck, the section of the pith or “trace”
of the dormant bud in the center.

In the wood of many broad-leaved trees the wood fibres
are much longer when full grown than when they are first
formed in the cambium or growing zone. This causes
the tips of each fibre to crowd in between the fibres above
and below, and leads to an irregular interlacement of these
fibres, which adds to the toughness, but reduces the cleavability
of the wood. At the juncture of the limb and stem
the fibres on the upper and lower sides of the limb behave[89]
differently. On the lower side they run from the stem
into the limb, forming an uninterrupted strand or tissue
and a perfect union. On the upper side the fibres bend
aside, are not continuous into the
limb, and hence the connection is
not perfect (see Fig. 18). Owing
to this arrangement of the fibres,
the cleft made in splitting never
runs into the knot if started on
the side above the limb, but is
apt to enter the knot if started
below, a fact well understood in
woodcraft. When limbs die, decay,
and break off, the remaining stubs
are surrounded, and may finally
be covered by the growth of the
trunk and thus give rise to the annoying
“dead” or “loose” knots.

Fig. 18. Section of Wood
showing Position of the
Grain at Base of a Limb.
P, pith of both stem and
limb; 1-7, seven yearly
layers of wood; a, b, knot
or basal part of a limb
which lived for four years,
then died and broke off
near the stem, leaving the
part to the left of a, b, a
“sound” knot, the part
to the right a “dead”
knot, which would soon
be entirely covered by
the growing stem.

COLOR AND ODOR
OF WOOD

Color, like structure, lends
beauty to the wood, aids in its
identification, and is of great value
in the determination of its quality.
If we consider only the heartwood,
the black color of the persimmon,
the dark brown of the walnut, the
light brown of the white oaks, the
reddish brown of the red oaks,
the yellowish white of the tulip
and poplars, the brownish red of
the redwood and cedars, the yellow
of the papaw and sumac, are all reliable
marks of distinction and color.
Together with luster and weight,
they are only too often the only features depended upon
in practice. Newly formed wood, like that of the outer few
rings, has but little color. The sapwood generally is light,[90]
and the wood of trees which form no heartwood changes
but little, except when stained by forerunners of disease.

The different tints of colors, whether the brown of oak,
the orange brown of pine, the blackish tint of walnut, or
the reddish cast of cedar, are due to pigments, while the
deeper shade of the summer-wood bands in pine, cedar,
oak, or walnut is due to the fact that the wood being
denser, more of the colored wood substance occurs on a
given space, i.e., there is more colored matter per square
inch. Wood is translucent, a thin disk of pine permitting
light to pass through quite freely. This translucency
affects the luster and brightness of lumber.

When lumber is attacked by fungi, it becomes more
opaque, loses its brightness, and in practice is designated
“dead,” in distinction to “live” or bright timber. Exposure
to air darkens all wood; direct sunlight and occasional
moistening hasten this change, and cause it to
penetrate deeper. Prolonged immersion has the same
effect, pine wood becoming a dark gray, while oak changes
to a blackish brown.

Odor, like color, depends on chemical compounds,
forming no part of the wood substance itself. Exposure
to weather reduces and often changes the odor,
but a piece of long-leaf pine, cedar, or camphor wood exhales
apparently as much odor as ever when a new surface
is exposed. Heartwood is more odoriferous than sapwood.
Many kinds of wood are distinguished by strong and
peculiar odors. This is especially the case with camphor,
cedar, pine, oak, and mahogany, and the list would comprise
every kind of wood in use were our sense of smell
developed in keeping with its importance.

Decomposition is usually accompanied by pronounced
odors. Decaying poplar emits a disagreeable odor, while
red oak often becomes fragrant, its smell resembling that
of heliotrope.[91]

WEIGHT OF WOOD

A small cross-section of wood (as in Fig. 19) dropped
into water sinks, showing that the substance of which
wood fibre or wood is built up is heavier than water. By
immersing the wood successively in
heavier liquids, until we find a liquid
in which it does not sink, and comparing
the weight of the same with water,
we find that wood substance is about
1.6 times as heavy as water, and that
this is as true of poplar as of oak or
pine.

Separating a single cell (as shown in
Fig. 20, a), drying and then dropping
it into water, it floats. The air-filled
cell cavity or interior reduces its weight,
and, like an empty corked bottle, it weighs less than the
water. Soon, however, water soaks into the cell, when it
fills up and sinks. Many such cells grown together,
as in a block of wood, when all or most
of them are filled with water, will float as long
as the majority of them are empty or only
partially filled. This is why a green, sappy pine
pole soon sinks in “driving” (floating down
stream). Its cells are largely filled before it is
thrown in, and but little additional water suffices
to make its weight greater than that of the
water. In a good-sized white pine log, composed
chiefly of empty cells (heartwood), the water
requires a very long time to fill up the cells (five
years would not suffice to fill them all), and
therefore the log may float for many months.
When the wall of the wood fibre is very thick
(five eighths or more of the volume, as in Fig.
20, b), the fibre sinks whether empty or filled.
This applies to most of the fibres of the dark
summer-wood bands in pines, and to the compact fibres
of oak or hickory, and many, especially tropical woods,[92]
have such thick-walled cells and so little empty or air space
that they never float.

Here, then, are the two main factors of weight in wood;
the amount of cell wall or wood substance constant for
any given piece, and the amount of water contained in
the wood, variable even in the standing tree, and only in
part eliminated in drying.

The weight of the green wood of any species varies
chiefly as a second factor, and is entirely misleading, if
the relative weight of different kinds is sought. Thus
some green sticks of the otherwise lighter cypress and
gum sink more readily than fresh oak.

The weight of sapwood or the sappy, peripheral part
of our common lumber woods is always great, whether
cut in winter or summer. It rarely falls much below
forty-five pounds, and commonly exceeds fifty-five pounds
to the cubic foot, even in our lighter wooded species. It
follows that the green wood of a sapling is heavier than
that of an old tree, the fresh wood from a disk of the upper
part of a tree is often heavier than that of the lower part,
and the wood near the bark heavier than that nearer the
pith; and also that the advantage of drying the wood
before shipping is most important in sappy and light
kinds.

When kiln-dried, the misleading moisture factor of
weight is uniformly reduced, and a fair comparison possible.
For the sake of convenience in comparison, the
weight of wood is expressed either as the weight per cubic
foot, or, what is still more convenient, as specific weight
or density. If an old long-leaf pine is cut up (as shown
in Fig. 21) the wood of disk No. 1 is heavier than that of
disk No. 2, the latter heavier than that of disk No. 3, and
the wood of the top disk is found to be only about three
fourths as heavy as that of disk No. 1. Similiarly, if disk
No. 2 is cut up, as in the figure, the specific weight of the
different parts is:

• a, about 0.52
• b, about 0.64
• c, about 0.67
• d, e, f,  about 0.65

showing that in this disk at least the wood formed during[93]
the many years’ growth, represented in piece a, is much
lighter than that of former years. It also shows that the
best wood is the middle part, with its large proportion of
dark summer bands.

Cutting up all disks in the same way, it will be found
that the piece a of the first disk is heavier than the piece
a of the fifth, and that piece c of the first disk excels the
piece c of all the other disks. This shows that the wood
grown during the same number of years is lighter in the
upper parts of the stem; and if the disks are smoothed on
the radial surfaces and set up one on top of the other in
their regular order, for the sake of comparison, this decrease
in weight will be seen to be accompanied by a decrease
in the amount of summer-wood. The color effect
of the upper disks is conspicuously lighter. If our old
pine had been cut one hundred and fifty years ago,
before the outer, lighter wood was laid on, it is evident
that the weight of the wood of any one disk would have
been found to increase from the center outward, and no
subsequent decrease could have been observed.[94]

In a thrifty young pine, then, the wood is heavier from
the center outward, and lighter from below upward; only
the wood laid on in old age falls in weight below the average.
The number of brownish bands of summer-wood are a
direct indication of these differences. If an old oak is
cut up in the same manner, the butt cut is also found
heaviest and the top lightest, but, unlike the disk of pine,
the disk of oak has its firmest wood at the center, and each
successive piece from the center outward is lighter than
its neighbor.

Examining the pieces, this difference is not as readily
explained by the appearance of each piece as in the case
of pine wood. Nevertheless, one conspicuous point appears
at once. The pores, so very distinct in oak, are
very minute in the wood near the center, and thus the
wood is far less porous.

Studying different trees, it is found that in the pines,
wood with narrow rings is just as heavy as and often heavier
than the wood with wider rings; but if the rings are unusually
narrow in any part of the disk, the wood has a
lighter color; that is, there is less summer-wood and therefore
less weight.

In oak, ash, or elm trees of thrifty growth, the rings,
fairly wide (not less than one-twelfth inch), always form
the heaviest wood, while any piece with very narrow rings
is light. On the other hand, the weight of a piece of hard
maple or birch is quite independent of the width of its
rings.

The bases of limbs (knots) are usually heavy, very
heavy in conifers, and also the wood which surrounds
them, but generally the wood of the limbs is lighter than
that of the stem, and the wood of the roots is the
lightest.

In general, it may be said that none of the native woods
in common use in this country are when dry as heavy as
water, i.e., sixty-two pounds to the cubic foot. Few exceed
fifty pounds, while most of them fall below forty
pounds, and much of the pine and other coniferous wood
weigh less than thirty pounds per cubic foot. The weight
of the wood is in itself an important quality. Weight[95]
assists in distinguishing maple from poplar. Lightness
coupled with great strength and stiffness recommends
wood for a thousand different uses. To a large extent
weight predicates the strength of the wood, at least in the
same species, so that a heavy piece of oak will exceed in
strength a light piece of the same species, and in pine it
appears probable that, weight for weight, the strength of
the wood of various pines is nearly equal.

Weight of Kiln-dried Wood of Different Species

“FIGURE” IN WOOD[96]

Many theories have been propounded as to the cause
of “figure” in timber; while it is true that all timber
possesses “figure” in some degree, which is more noticeable
if it be cut in certain ways, yet there are some woods in
which it is more conspicuous than in others, and which
for cabinet or furniture work are much appreciated, as
it adds to the value of the work produced.

The characteristic “figure” of oak is due to the broad
and deep medullary rays so conspicuous in this timber,
and the same applies to honeysuckle. Figure due to the
same cause is found in sycamore and beech, but is not so
pronounced. The beautiful figure in “bird’s eye maple”
is supposed to be due to the boring action of insects in
the early growth of the tree, causing pits or grooves, which
in time become filled up by being overlain by fresh layers
of wood growth; these peculiar and unique markings
are found only in the older and inner portion of the tree.

Pitch pine has sometimes a very beautiful “figure,” but
it generally does not go deep into the timber; walnut has
quite a variety of “figures,” and so has the elm. It is in
mahogany, however, that we find the greatest variety of
“figure,” and as this timber is only used for furniture and
fancy work, a good “figure” greatly enhances its value,
as firmly figured logs bring fancy prices.

Mahogany, unlike the oak, never draws its “figure” from
its small and almost unnoticeable medullary rays, but
from the twisted condition of its fibres; the natural growth
of mahogany produces a straight wood; what is called
“figured” is unnatural and exceptional, and thus adds
to its value as an ornamental wood. These peculiarities
are rarely found in the earlier portion of the tree that is
near the center, being in this respect quite different from
maple; they appear when the tree is more fully developed,
and consist of bundles of woody fibres which, instead of
being laid in straight lines, behave in an erratic manner
and are deposited in a twisted form; sometimes it may
be caused by the intersection of branches, or possibly by
the crackling of the bark pressing on the wood, and thus[97]
moving it out of its natural straight course, causing a
wavy line which in time becomes accentuated.

It will have been observed by most people that the outer
portion of a tree is often indented by the bark, and the
outer rings often follow a sinuous course which corresponds
to this indention, but in most trees, after a few years, this
is evened up and the annual rings assume their nearly
circular form; it is supposed by some that in the case of
mahogany this is not the case, and that the indentations
are even accentuated.

The best figured logs of timber are secured from trees
which grow in firm rocky soil; those growing on low-lying
or swampy ground are seldom figured. To the practical
woodworker the figure in mahogany causes some difficulty
in planing the wood to a smooth surface; some portions
plane smooth, others are the “wrong way of the grain.”

Figure in wood is effected by the way light is thrown
upon it, showing light if seen from one direction, and dark
if viewed from another, as may easily be observed by holding
a piece of figured mahogany under artificial light and
looking at it from opposite directions. The characteristic
markings on mahogany are “mottle,” which is also
found in sycamore, and is conspicuous on the backs of
fiddles and violins, and is not in itself valuable; it runs
the transverse way of the fibres and is probably the effect
of the wind upon the tree in its early stages of growth.
“Roe,” which is said to be caused by the contortion of
the woody fibres, and takes a wavy line parallel to them,
is also found in the hollow of bent stems and in the root
structure, and when combined with “mottle” is very
valuable. “Dapple” is an exaggerated form of mottle.
“Thunder shake,” “wind shake,” or “tornado shake” is
a rupture of the fibres across the grain, which in mahogany
does not always break them; the tree swaying in the wind
only strains its fibres, and thus produces mottle in the wood.

SECTION V[98]

ENEMIES OF WOOD

From the writer’s personal investigations of this subject
in different sections of the country, the damage to
forest products of various kinds from this cause seems
to be far more extensive than is generally recognized.
Allowing a loss of five per cent on the total value of the
forest products of the country, which the writer believes
to be a conservative estimate, it would amount to something
over $30,000,000 annually. This loss differs from
that resulting from insect damage to natural forest resources,
in that it represents more directly a loss of money
invested in material and labor. In dealing with the insects
mentioned, as with forest insects in general, the
methods which yield the best results are those which relate
directly to preventing attack, as well as those which are
unattractive or unfavorable. The insects have two objects
in their attack: one is to obtain food, the other is to prepare
for the development of their broods. Different
species of insects have special periods during the season
of activity (March to November), when the adults are
on the wing in search of suitable material in which to
deposit their eggs. Some species, which fly in April, will
be attracted to the trunks of recently felled pine trees or
to piles of pine sawlogs from trees felled the previous
winter. They are not attracted to any other kind of
timber, because they can live only in the bark or wood
of pine, and only in that which is in the proper condition
to favor the hatching of their eggs and the normal development
of their young. As they fly only in April,
they cannot injure the logs of trees felled during the remainder
of the year.[99]

There are also oak insects, which attack nothing but
oak; hickory, cypress, and spruce insects, etc., which have
different habits and different periods of flight, and require
special conditions of the bark and wood for depositing
their eggs or for subsequent development of their broods.
Some of these insects have but one generation in a year,
others have two or more, while some require more than
one year for the complete development and transformation.
Some species deposit their eggs in the bark or wood of
trees soon after they are felled or before any perceptible
change from the normal living tissue has taken place;
other species are attracted only to dead bark and dead
wood of trees which have been felled or girdled for several
months; others are attracted to dry and seasoned wood;
while another class will attack nothing but very old, dry
bark or wood of special kinds and under special conditions.
Thus it will be seen how important it is for the
practical man to have knowledge of such of the foregoing
facts as apply to his immediate interest in the manufacture
or utilization of a given forest product, in order that he
may with the least trouble and expense adjust his business
methods to meet the requirements for preventing
losses.

The work of different kinds of insects, as represented
by special injuries to forest products, is the first thing to
attract attention, and the distinctive character of this
work is easily observed, while the insect responsible for
it is seldom seen, or it is so difficult to determine by the
general observer from descriptions or illustrations that
the species is rarely recognized. Fortunately, the character
of the work is often sufficient in itself to identify the cause
and suggest a remedy, and in this section primary consideration
is given to this phase of the subject.

Ambrosia or Timber Beetles

The characteristic work of this class of wood-boring
beetles is shown in Figs. 22 and 23. The injury consists
of pinhole and stained-wood defects in the sapwood and
heartwood of recently felled or girdled trees, sawlogs,
pulpwood, stave and shingle bolts, green or unseasoned[100]
lumber, and staves and heads of barrels containing alcoholic
liquids. The holes and galleries are made by the
adult parent beetles, to serve as entrances and temporary
houses or nurseries for the development of their broods
of young, which feed on a fungus growing on the walls of
the galleries.

The growth of this ambrosia-like fungus is induced
and controlled by the parent beetles, and the young are[101]
dependent upon it for food. The wood must be in exactly
the proper condition for the growth of the fungus
in order to attract the beetles and induce them to excavate
their galleries; it must have a certain degree of moisture
and other favorable qualities, which usually prevail during
the period involved in the change from living, or normal,
to dead or dry wood; such a condition is found in recently
felled trees, sawlogs, or like crude products.

There are two general types or classes of these galleries:
one in which the broods develop together in the main
burrows (see Fig. 22), the other in which the individuals
develop in short, separate side chambers, extending at
right angles from the primary galleries (see Fig. 23). The
galleries of the latter type are usually accompanied by a
distinct staining of the wood, while those of the former
are not.

The beetles responsible for this work are cylindrical in
form, apparently with a head (the prothorax) half as long
as the remainder of the body (see Figs. 22, a, and 23, a).

North American species vary in size from less than
one-tenth to slightly more than two-tenths of an inch,
while some of the subtropical and tropical species attain
a much larger size. The diameter of the holes made by
each species corresponds closely to that of the body, and
varies from about one-twentieth to one-sixteenth of an
inch for the tropical species.

Round-headed Borers

The character of the work of this class of wood- and bark-boring
grubs is shown in Fig. 24. The injuries consist
of irregular flattened or nearly round wormhole defects
in the wood, which sometimes result in the destruction[102]
of valuable parts of the wood or bark material. The sapwood
and heartwood of recently felled trees, sawlogs,
poles posts, mine props, pulpwood and cordwood, also
lumber or square timber, with bark on the edges, and
construction timber in new and old buildings, are injured
by wormhole defects, while the valuable parts of stored
oak and hemlock tanbark and certain kinds of wood are
converted into worm-dust. These injuries are caused
by the young or larvae of long-horned beetles. Those
which infest the wood hatch from eggs deposited in the
outer bark of logs and like material, and the minute grubs
hatching therefrom bore into the inner bark, through
which they extend their irregular burrows, for the purpose
of obtaining food from the sap and other nutritive material
found in the plant tissue. They continue to extend and
enlarge their burrows as they increase in size, until they
are nearly or quite full grown. They then enter the wood
and continue their excavations deep into the sapwood or
heartwood until they attain their normal size. They
then excavate pupa cells in which to transform into adults,[103]
which emerge from the wood through exit holes in the
surface. This class of borers is represented by a large
number of species. The adults, however, are seldom seen
by the general observer unless cut out of the wood before
they have emerged.

Flat-headed Borers

The work of the flat-headed borers (Fig. 24) is only
distinguished from that of the preceding by the broad,
shallow burrows, and the much more oblong form of the
exit holes. In general, the injuries are similiar, and effect
the same class of products, but they are of much less importance.
The adult forms are flattened, metallic-colored
beetles, and represent many species, of various sizes.

Timber Worms

The character of the work done by this class is shown
in Fig. 25. The injury consists of pinhole defects in the
sapwood and heartwood of felled trees, sawlogs and like
material which have been left in the woods or in piles in the
open for several months during the warmer seasons. Stave[104]
and shingle bolts and closely piled oak lumber and square
timbers also suffer from injury of this kind. These injuries
are made by elongate, slender worms or larvae,
which hatch from eggs deposited by the adult beetles in the
outer bark, or, where there is no bark, just beneath the
surface of the wood. At first the young larvae bore
almost invisible holes for a long distance through the sapwood
and heartwood, but as they increase in size the same
holes are enlarged and extended until the larvae have attained
their full growth. They then transform to adults,
and emerge through the enlarged entrance burrows. The
work of these timber worms is distinguished from that of
the timber beetles by the greater variation in the size of
holes in the same piece of wood, also by the fact that they
are not branched from a single entrance or gallery, as are
those made by the beetles.

Powder Post Borers

The character of the work of this class of insects is
shown in Figs. 26, 27, and 28. The injury consists of
closely placed burrows, packed
with borings, or a completely
destroyed or powdered condition
of the wood of seasoned products,
such as lumber, crude and
finished handle and wagon stock,
cooperage and wooden truss
hoops, furniture, and inside finish
woodwork, in old buildings, as
well as in many other crude or
finished and utilized woods.
This is the work of both the
adults and young stages of some
species, or of the larval stage
alone of others. In the former,
the adult beetles deposit their
eggs in burrows or galleries excavated
for the purpose, as in
Figs. 26 and 27, while in the
latter (Fig. 28) the eggs are on
or beneath the surface of the
wood. The grubs complete the
destruction by boring through
the solid wood in all directions
and packing their burrows with
the powdered wood. When they
are full grown they transform to
the adult, and emerge from the
injured material through holes in
the surface. Some of the species
continue to work in the same
wood until many generations
have developed and emerged or
until every particle of wood
tissue has been destroyed and the available nutritive substance
extracted.

Fig. 28. Work of Powder Post
Beetles, Lyctus striatus, in
Hickory Handles and Spokes.
a, larva; b, pupa; c, adult;
d, exit holes; e, entrance of
larvae (vents for borings are
exits of parasites); f, work
of larvae; g, wood, completely
destroyed; h, sapwood;
i, heartwood.[106]

Conditions Favorable for Insect Injury—Crude Products—Round
Timber with Bark on

Newly felled trees, sawlogs, stave and heading bolts,
telegraph poles, posts, and the like material, cut in the
fall and winter, and left on the ground or in close piles
during a few weeks or months in the spring or summer,
causing them to heat and sweat, are especially liable to
injury by ambrosia beetles (Figs. 22 and 23), round and
flat-headed borers (Fig. 24), and timber worms (Fig. 25),
as are also trees felled in the warm season, and left for a
time before working up into lumber.

The proper degree of moisture found in freshly cut
living or dying wood, and the period when the insects are
flying, are the conditions most favorable for attack. This
period of danger varies with the time of the year the timber
is felled and with the different kinds of trees. Those
felled in late fall and winter will generally remain attractive
to ambrosia beetles, and to the adults of round- and
flat-headed borers during March, April, and May.
Those felled in April to September may be attacked in
a few days after they are felled, and the period of danger
may not extend over more than a few weeks. Certain
kinds of trees felled during certain months and seasons
are never attacked, because the danger period prevails
only when the insects are flying; on the other hand, if
the same kinds of trees are felled at a different time, the
conditions may be most attractive when the insects are
active, and they will be thickly infested and ruined.

The presence of bark is absolutely necessary for infestation
by most of the wood-boring grubs, since the eggs
and young stages must occupy the outer and inner portions
before they can enter the wood. Some ambrosia
and timber worms will, however, attack barked logs,
especially those in close piles, and others shaded and
protected from rapid drying.

The sapwood of pine, spruce, fir, cedar, cypress, and
the like softwoods is especially liable to injury by ambrosia
beetles, while the heartwood is sometimes ruined by a
class of round-headed borers, known as “sawyers.” Yellow[107]
poplar, oak, chestnut, gum, hickory, and most other
hardwoods are as a rule attacked by species of ambrosia
beetles, sawyers, and timber worms, different from those
infesting the pines, there being but very few species which
attack both.

Mahogany and other rare and valuable woods imported
from the tropics to this country in the form of round logs,
with or without bark on, are commonly damaged more
or less seriously by ambrosia beetles and timber worms.

It would appear from the writer’s investigations of
logs received at the mills in this country, that the principal
damage is done during a limited period—from the
time the trees are felled until they are placed in fresh or
salt water for transportation to the shipping points. If,
however, the logs are loaded on a vessel direct from the
shore, or if not left in the water long enough to kill the
insects, the latter will continue their destructive work
during transportation to other countries and after they
arrive, and until cold weather ensues or the logs are converted
into lumber.

It was also found that a thorough soaking in sea-water,
while it usually killed the insects at the time, did not prevent
subsequent attacks by both foreign and native ambrosia
beetles; also, that the removal of the bark from such
logs previous to immersion did not render them entirely
immune. Those with the bark off were attacked more
than those with it on, owing to a greater amount of saline
moisture retained by the bark.

How to Prevent Injury

From the foregoing it will be seen that some requisites
for preventing these insect injuries to round timber are:

Saplings

Saplings, including hickory and other round hoop-poles
and similiar products, are subject to serious injuries and
destruction by round- and flat-headed borers (Fig. 24),
and certain species of powder post borers (Figs. 26 and 27)
before the bark and wood are dead or dry, and also by
other powder post borers (Fig. 28) after they are dried and[109]
seasoned. The conditions favoring attack by the former
class are those resulting from leaving the poles in piles
or bundles in or near the forest for a few weeks during the
season of insect activity, and by the latter from leaving
them stored in one place for several months.

Stave, Heading and Shingle Bolts

These are attacked by ambrosia beetles (Figs. 22 and
23), and the oak timber worm (Fig. 25, a), which, as has
been frequently reported, cause serious losses. The conditions
favoring attack by these insects are similiar to
those mentioned under “Round Timber.” The insects
may enter the wood before the bolts are cut from the log
or afterward, especially if the bolts are left in moist, shady
places in the woods, in close piles during the danger period.
If cut during the warm season, the bark should be removed
and the bolts converted into the smallest practicable
size and piled in such manner as to facilitate rapid
drying.

Unseasoned Products in the Rough

Freshly sawn hardwood, placed in close piles during
warm, damp weather in July and September, presents
especially favorable conditions for injury by ambrosia
beetles (Figs. 22, a, and 23, a). This is due to the continued
moist condition of such material.

Heavy two-inch or three-inch stuff is also liable to attack
even in loose piles with lumber or cross sticks. An
example of the latter was found in a valuable lot of mahogany
lumber of first grade, the value of which was
reduced two thirds by injury from a native ambrosia
beetle. Numerous complaints have been received from
different sections of the country of this class of injury to
oak, poplar, gum, and other hardwoods. In all cases it
is the moist condition and retarded drying of the lumber
which induces attack; therefore, any method which will
provide for the rapid drying of the wood before or after
piling will tend to prevent losses.

It is important that heavy lumber should, as far as
possible, be cut in the winter months and piled so that it[110]
will be well dried out before the middle of March. Square
timber, stave and heading bolts, with the bark on, often
suffer from injuries by flat- or round-headed borers, hatching
from eggs deposited in the bark of the logs before they
are sawed and piled. One example of serious damage
and loss was reported in which white pine staves for paint
buckets and other small wooden vessels, which had been
sawed from small logs, and the bark left on the edges,
were attacked by a round-headed borer, the adults having
deposited their eggs in the bark after the stock was sawn
and piled. The character of the injury is shown in Fig. 29.
Another example was reported from a manufacturer in
the South, where the pieces of lumber which had strips
of bark on one side were seriously damaged by the same
kind of borer, the eggs having been deposited in the logs
before sawing or in the bark after the lumber was piled.
If the eggs are deposited in the logs, and the borers have
entered the inner bark or the wood before sawing, they
may continue their work regardless of methods of piling,
but if such lumber is cut from new logs and placed in the
pile while green, with the bark surface up, it will be much
less liable to attack than if piled with the bark edges down.
This liability of lumber with bark edges or sides to be
attacked by insects suggests the importance of the removal
of the bark, to prevent damage, or, if this is not
practicable, the lumber with the bark on the sides should
be piled in open, loose piles with the bark up, while that
with the bark on the edges should be placed on the outer
edges of the piles, exposed to the light and air.

Fig. 29. Work of Round-headed Borers, Callidium antennatum, in White
Pine Bucket Staves from New Hampshire. a, where egg was deposited
in bark; b, larval mine; c, pupal cell; d, exit in bark; e, adult.

In the Southern States it is difficult to keep green timber
in the woods or in piles for any length of time, because of
the rapidity which wood-destroying fungi attack it. This
is particularly true during the summer season, when the
humidity is greatest. There is really no easily-applied,
general specific for these summer troubles in the handling
of wood, but there are some suggestions that are worth
while that it may be well to mention. One of these, and
the most important, is to remove all the bark from the
timber that has been cut, just as soon as possible after
felling. And, in this, emphasis should be laid on the ALL,[111]
as a piece of bark no larger than a man’s little finger will
furnish an entering place for insects, and once they get in,
it is a difficult matter to get rid of them, for they seldom
stop boring until they ruin the stick. And again, after
the timber has been felled and the bark removed, it is
well to get it to the mill pond or cut up into merchantable
sizes and on to the pile as soon as possible. What is
wanted is to get the timber up off the ground, to a
place where it can get plenty of air, to enable the sap
to dry up before it sours; and, besides, large units of
wood are more likely to crack open on the ends from the[112]
heat than they would if cut up into the smaller units
for merchandizing.

A moist condition of lumber and square timber, such
as results from close or solid piles, with the bottom layers
on the ground or on foundations of old decaying logs or
near decaying stumps and logs, offers especially favorable
conditions for the attack of white ants.

Seasoned Products in the Rough

Seasoned or dry timber in stacks or storage is liable to
injury by powder post borers (Fig. 28). The conditions
favoring attack are: (1) The presence of a large
proportion of sapwood, as in hickory, ash, and similiar
woods; (2) material which is two or more years old, or
that which has been kept in one place for a long time;
(3) access to old infested material. Therefore, such stock
should be frequently examined for evidence of the presence
of these insects. This is always indicated by fine, flour-like
powder on or beneath the piles, or otherwise associated
with such material. All infested material should be at
once removed and the infested parts destroyed by burning.

Dry Cooperage Stock and Wooden Truss Hoops

These are especially liable to attack and serious injury
by powder post borers (Fig. 28), under the same or similiar
conditions as the preceding.

Staves and Heads of Barrels containing
Alcoholic Liquids

These are liable to attack by ambrosia beetles (Figs.
22, a, and 23, a), which are attracted by the moist condition
and possibly by the peculiar odor of the wood, resembling
that of dying sapwood of trees and logs, which
is their normal breeding place.

There are many examples on record of serious losses
of liquors from leakage caused by the beetles boring through
the staves and heads of the barrels and casks in cellars
and storerooms.

The condition, in addition to the moisture of the wood,
which is favorable for the presence of the beetles, is proximity[113]
to their breeding places, such as the trunks and
stumps of recently felled or dying oak, maple, and other
hardwood or deciduous trees; lumber yards, sawmills,
freshly-cut cordwood, from living or dead trees, and forests
of hardwood timber. Under such conditions the beetles
occur in great numbers, and if the storerooms and cellars
in which the barrels are kept stored are damp, poorly ventilated,
and readily accessible to them, serious injury is
almost certain to follow.

SECTION VI[114]

WATER IN WOOD

DISTRIBUTION OF WATER IN WOOD

Local Distribution of Water in Wood

As seasoning means essentially the more or less rapid
evaporation of water from wood, it will be necessary to discuss at the very outset where water is found in wood,
and its local seasonal distribution in a tree.

Water may occur in wood in three conditions: (1) It
forms the greater part (over 90 per cent) of the protoplasmic
contents of the living cells; (2) it saturates the
walls of all cells; and (3) it entirely or at least partly fills
the cavities of the lifeless cells, fibres, and vessels.

In the sapwood of pine it occurs in all three forms; in
the heartwood only in the second form, it merely saturates
the walls.

Of 100 pounds of water associated with 100 pounds of
dry wood substance taken from 200 pounds of fresh sapwood
of white pine, about 35 pounds are needed to saturate
the cell walls, less than 5 pounds are contained in the
living cells, and the remaining 60 pounds partly fill the
cavities of the wood fibres. This latter forms the sap
as ordinarily understood.

The wood next to the bark contains the most water.
In the species which do not form heartwood, the decrease
toward the pith is gradual, but where heartwood is formed
the change from a more moist to a drier condition is usually
quite abrupt at the sapwood limit.

In long-leaf pine, the wood of the outer one inch of a
disk may contain 50 per cent of water, that of the next,
or the second inch, only 35 per cent, and that of the heartwood,[115]
only 20 per cent. In such a tree the amount of
water in any one section varies with the amount of sapwood,
and is greater for the upper than the lower cuts,
greater for the limbs than the stems, and greatest of all
in the roots.

Different trees, even of the same kind and from the
same place, differ as to the amount of water they contain.
A thrifty tree contains more water than a stunted one,
and a young tree more than on old one, while the wood
of all trees varies in its moisture relations with the season
of the year.

Seasonal Distribution of Water in Wood

It is generally supposed that trees contain less water
in winter than in summer. This is evidenced by the
popular saying that “the sap is down in the winter.” This
is probably not always the case; some trees contain as
much water in winter as in summer, if not more. Trees
normally contain the greatest amount of water during
that period when the roots are active and the leaves are
not yet out. This activity commonly begins in January,
February, and March, the exact time varying with the
kind of timber and the local atmospheric conditions. And
it has been found that green wood becomes lighter or
contains less water in late spring or early summer, when
transpiration through the foliage is most rapid. The
amount of water at any one season, however, is doubtless
much influenced by the amount of moisture in the soil.
The fact that the bark peels easily in the spring depends
on the presence of incomplete, soft tissue found between
wood and bark during this season, and has little to do
with the total amount of water contained in the wood of
the stem.

Even in the living tree a flow of sap from a cut occurs
only in certain kinds of trees and under special circumstances.
From boards, felled timber, etc., the water
does not flow out, as is sometimes believed, but must be
evaporated. The seeming exceptions to this rule are
mostly referable to two causes; clefts or “shakes” will[116]
allow water contained in them to flow out, and water is
forced out of sound wood, if very sappy, whenever the
wood is warmed, just as water flows from green wood when
put in a stove.

Composition of Sap

The term “sap” is an ambiguous expression. The
sap in the tree descends through the bark, and except
in early spring is not present in the wood of the tree
except in the medullary rays and living tissues in the
“sapwood.”

What flows through the “sapwood” is chiefly water
brought from the soil. It is not pure water, but contains
many substances in solution, such as mineral salts, and
in certain species—maple, birch, etc., it also contains
at certain times a small percentage of sugar and other
organic matter.

The water rises from the roots through the sapwood to
the leaves, where it is converted into true “sap” which
descends through the bark and feeds the living tissues
between the bark and the wood, which tissues make the
annual growth of the trunk. The wood itself contains
very little true sap and the heartwood none.

The wood contains, however, mineral substances, organic
acids, volatile oils and gums, as resin, cedar oil, etc.

All the conifers—pines, cedars, junipers, cypresses,
sequoias, yews, and spruces—contain resin. The sap
of deciduous trees—those which shed their leaves at
stated seasons—is lacking in this element, and its constituents
vary greatly in the different species. But there
is one element common to all trees, and for that matter
to almost all plant growth, and that is albumen.

Both resin and albumen, as they exist in the sap of
woods, are soluble in water; and both harden with heat,
much the same as the white of an egg, which is almost
pure albumen.

These organic substances are the dissolved reserve food,
stored during the winter in the pith rays, etc., of the wood
and bark; generally but a mere trace of them is to be
found. From this it appears that the solids contained[117]
in the sap, such as albumen, gum, sugar, etc., cannot
exercise the influence on the strength of the wood which is
so commonly claimed for them.

Effects of Moisture on Wood

The question of the effect of moisture upon the strength
and stiffness of wood offers a wide scope for study, and
authorities consulted differ in conclusions. Two authorities
give the tensile strength in pounds per square inch
for white oak as 10,000 and 19,500, respectively; for
spruce, 8,000 to 19,500, and other species in similiar startling
contrasts.

Wood, we are told, is composed of organic products.
The chief material is cellulose, and this in its natural state
in the living plant or green wood contains from 25 to 35
per cent of its weight in moisture. The moisture renders
the cellulose substance pliable. What the physical action
of the water is upon the molecular structure of organic
material, to render it softer and more pliable, is largely
a matter of conjecture.

The strength of a timber depends not only upon its
relative freedom from imperfections, such as knots, crookedness
of grain, decay, wormholes or ring-shakes, but also
upon its density; upon the rate at which it grew, and
upon the arrangement of the various elements which
compose it.

The factors effecting the strength of wood are therefore
of two classes: (1) Those inherent in the wood itself and
which may cause differences to exist between two pieces
from the same species of wood or even between the two
ends of a piece, and (2) those which are foreign to the wood
itself, such as moisture, oils, and heat.

Though the effect of moisture is generally temporary,
it is far more important than is generally realized. So
great, indeed, is the effect of moisture that under some
conditions it outweighs all the other causes which effect
strength, with the exception, perhaps of decided imperfections
in the wood itself.[118]

The Fibre Saturation Point in Wood

Water exists in green wood in two forms: (1) As liquid
water contained in the cavities of the cells or pores, and
(2) as “imbibed” water intimately absorbed in the substance
of which the wood is composed. The removal of
the free water from the cells or pores will evidently have
no effect upon the physical properties or shrinkage of the
wood, but as soon as any of the “imbibed” moisture is
removed from the cell walls, shrinkage begins to take place
and other changes occur. The strength also begins to
increase at this time.

The point where the cell walls or wood substance becomes
saturated is called the “fibre saturation point,”
and is a very significant point in the drying of wood.

It is easy to remove the free water from woods which
will stand a high temperature, as it is only necessary to
heat the wood slightly above the boiling point in a closed
vessel, which will allow the escape of the steam as it is
formed, but will not allow dry air to come in contact with
the wood, so that the surface will not become dried below
its saturation point. This can be accomplished with
most of the softwoods, but not as a rule with the hardwoods,
as they are injured by the temperature necessary.

The chief difficulties are encountered in evaporating
the “imbibed” moisture and also where the free water
has to be removed through its gradual transfusion instead
of boiling. As soon as the imbibed moisture begins to
be extracted from any portion, shrinkage takes place and
stresses are set up in the wood which tend to cause checking.

The fibre saturation point lies between moisture conditions
of 25 and 30 per cent of the dry weight of the
wood, depending on the species. Certain species of eucalyptus,
and probably other woods, however, appear to
be exceptional in this respect, in that shrinkage begins
to take place at a moisture condition of 80 to 90 per cent
of the dry weight.

SECTION VII[119]

WHAT SEASONING IS

Seasoning is ordinarily understood to mean drying.
When exposed to the sun and air, the water in green wood
rapidly evaporates. The rate of evaporation will depend
on: (1) the kind of wood; (2) the shape and thickness of
the timber; and (3) the conditions under which the wood
is placed or piled.

Pieces of wood completely surrounded by air, exposed
to the wind and the sun, and protected by a roof from
rain and snow, will dry out very rapidly, while wood piled
or packed close together so as to exclude the air, or left
in the shade and exposed to rain and snow, will dry out
very slowly and will also be subject to mould and decay.

But seasoning implies other changes besides the evaporation
of water. Although we have as yet only a vague
conception as to the exact nature of the difference between
seasoned and unseasoned wood, it is very probable that
one of these consists in changes in the albuminous substances
in the wood fibres, and possibly also in the tannins,
resins, and other incrusting substances. Whether the
change in these substances is merely a drying-out, or
whether it consists in a partial decomposition is at yet
undetermined. That the change during the seasoning
process is a profound one there can be no doubt, because
experience has shown again and again that seasoned wood
fibre is very much more permeable, both for liquids and
gases than the living, unseasoned fibre.

One can picture the albuminous substances as forming
a coating which dries out and possibly disintegrates when
the wood dries. The drying-out may result in considerable
shrinkage, which may make the wood fibre more
porous. It is also possible that there are oxidizing influences[120]
at work within these substances which result in
their disintegration. Whatever the exact nature of the
change may be, one can say without hesitation that exposure
to the wind and air brings about changes in the
wood, which are of such a nature that the wood becomes
drier and more permeable.

When seasoned by exposure to live steam, similiar
changes may take place; the water leaves the wood in the
form of steam, while the organic compounds in the walls
probably coagulate or disintegrate under the high temperature.

The most effective seasoning is without doubt that
obtained by the uniform, slow drying which takes place
in properly constructed piles outdoors, under exposure
to the winds and the sun and under cover from the rain
and snow, and is what has been termed “air-seasoning.”
By air-seasoning oak and similiar hardwoods, nature performs
certain functions that cannot be duplicated by any
artificial means. Because of this, woods of this class
cannot be successfully kiln-dried green from the saw.

In drying wood, the free water within the cells passes
through the cell walls until the cells are empty, while the
cell walls remain saturated. When all the free water has
been removed, the cell walls begin to yield up their moisture.
Heat raises the absorptive power of the fibres and
so aids the passage of water from the interior of the cells.
A confusion in the word “sap” is to be found in many
discussions of kiln-drying; in some instances it means
water, in other cases it is applied to the organic substances
held in a water solution in the cell cavities. The term is
best confined to the organic substances from the living
cell. These substances, for the most part of the nature
of sugar, have a strong attraction for water and water
vapor, and so retard drying and absorb moisture into
dried wood. High temperatures, especially those produced
by live steam, appear to destroy these organic compounds
and therefore both to retard and to limit the
reabsorption of moisture when the wood is subsequently
exposed to the atmosphere.

Air-dried wood, under ordinary atmospheric temperatures,[121]
retains from 10 to 20 per cent of moisture, whereas
kiln-dried wood may have no more than 5 per cent as it
comes from the kiln. The exact figures for a given species
depend in the first case upon the weather conditions, and
in the second case upon the temperature in the kiln and
the time during which the wood is exposed to it. When
wood that has been kiln-dried is allowed to stand in the
open, it apparently ceases to reabsorb moisture from the
air before its moisture content equals that of wood which
has merely been air-dried in the same place, and under
the same conditions, in other words kiln-dried wood will
not absorb as much moisture as air-dried wood under the
same conditions.

Difference between Seasoned and Unseasoned Wood

Although it has been known for a long time that there
is a marked difference in the length of life of seasoned and
of unseasoned wood, the consumers of wood have shown
very little interest in its seasoning, except for the purpose
of doing away with the evils which result from checking,
warping, and shrinking. For this purpose both kiln-drying
and air-seasoning are largely in use.

The drying of material is a subject which is extremely
important to most industries, and in no industry is it of
more importance than in the lumber trade. Timber
drying means not only the extracting of so much water,
but goes very deeply into the quality of the wood, its
workability and its cell strength, etc.

Kiln-drying, which dries the wood at a uniformly rapid
rate by artificially heating it in inclosed rooms, has become
a part of almost every woodworking industry, as
without it the construction of the finished product would
often be impossible. Nevertheless much unseasoned or
imperfectly seasoned wood is used, as is evidenced by the
frequent shrinkage and warping of the finished articles.
This is explained to a certain extent by the fact that the
manufacturer is often so hard pressed for his product that
he is forced to send out an inferior article, which the consumer
is willing to accept in that condition rather than[122]
to wait several weeks or months for an article made up
of thoroughly seasoned material, and also that dry kilns
are at present constructed and operated largely without
thoroughgoing system.

Forms of kilns and mode of operation have commonly
been copied by one woodworking plant after the example of
some neighboring establishment. In this way it has been
brought about that the present practices have many shortcomings.
The most progressive operators, however, have
experimented freely in the effort to secure special results
desirable for their peculiar products. Despite the diversity
of practice, it is possible to find among the larger and more
enterprising operators a measure of agreement, as to both
methods and results, and from this to outline the essentials
of a correct theory. As a result, properly seasoned wood
commands a high price, and in some cases cannot be obtained
at all.

Wood seasoned out of doors, which by many is supposed
to be much superior to kiln-dried material, is becoming
very scarce, as the demand for any kind of wood is so great
that it is thought not to pay to hold it for the time necessary
to season it properly. How long this state of affairs
is going to last it is difficult to say, but it is believed that
a reaction will come when the consumer learns that in
the long run it does not pay to use poorly seasoned material.
Such a condition has now arisen in connection with another
phase of the seasoning of wood; it is a commonly accepted
fact that dry wood will not decay nearly so fast as wet
or green wood; nevertheless, the immense superiority of
seasoned over unseasoned wood for all purposes where
resistance to decay is necessary has not been sufficiently
recognized. In the times when wood of all kinds was
both plentiful and cheap, it mattered little in most cases
how long it lasted or resisted decay. Wood used for
furniture, flooring, car construction, cooperage, etc., usually
got some chance to dry out before or after it was placed
in use. The wood which was exposed to decaying influences
was generally selected from those woods which,
whatever their other qualities might be, would resist decay
longest.[123]

To-day conditions have changed, so that wood can no
longer be used to the same extent as in former years.
Inferior woods with less lasting qualities have been pressed
into service. Although haphazard methods of cutting
and subsequent use are still much in vogue, there are
many signs that both lumbermen and consumers are
awakening to the fact that such carelessness and wasteful
methods of handling wood will no longer do, and must
give way to more exact and economical methods. The
reason why many manufacturers and consumers of wood
are still using the older methods is perhaps because of
long custom, and because they have not yet learned that,
though the saving to be obtained by the application of
good methods has at all times been appreciable, now,
when wood is more valuable, a much greater saving is
possible. The increased cost of applying economical
methods is really very slight, and is many times exceeded
by the value of the increased service which can be secured
through its use.

Manner of Evaporation of Water

The evaporation of water from wood takes place largely
through the ends, i.e., in the direction of the longitudinal
axis of the wood fibres. The evaporation from the other
surfaces takes place very slowly out of doors, and with
greater rapidity in a dry kiln. The rate of evaporation
differs both with the kind of timber and its shape; that is,
thin material will dry more rapidly than heavier stock.
Sapwood dries faster than heartwood, and pine more
rapidly than oak or other hardwoods.

Tests made show little difference in the rate of evaporation
in sawn and hewn stock, the results, however, not
being conclusive. Air-drying out of doors takes from
two months to a year, the time depending on the kind of
timber, its thickness, and the climatic conditions. After
wood has reached an air-dry condition it absorbs water
in small quantities after a rain or during damp weather,
much of which is immediately lost again when a few warm,
dry days follow. In this way wood exposed to the weather[124]
will continue to absorb water and lose it for indefinite
periods.

When soaked in water, seasoned woods absorb water
rapidly. This at first enters into the wood through the
cell walls; when these are soaked, the water will fill the
cell lumen, so that if constantly submerged the wood may
become completely filled with water.

The following figures show the gain in weight by absorption
of several coniferous woods, air-dry at the start,
expressed in per cent of the kiln-dry weight:

Absorption of Water by Dry Wood

Rapidity of Evaporation

The rapidity with which water is evaporated, that is,
the rate of drying, depends on the size and shape of the
piece and on the structure of the wood. An inch board
dries more than four times as fast as a four-inch plank, and
more than twenty times as fast as a ten-inch timber.
White pine dries faster than oak. A very moist piece of
pine or oak will, during one hour, lose more than four times
as much water per square inch from the cross-section, but
only one half as much from the tangential as from the radial
section. In a long timber, where the ends or cross-sections
form but a small part of the drying surface, this difference[125]
is not so evident. Nevertheless, the ends dry
and shrink first, and being opposed in this shrinkage by
the more moist adjoining parts, they check, the cracks
largely disappearing as seasoning progresses.

High temperatures are very effective in evaporating
the water from wood, no matter how humid the air, and
a fresh piece of sapwood may lose weight in boiling water,
and can be dried to quite an extent in hot steam.

In drying chemicals or fabrics, all that is required is to
provide heat enough to vaporize the moisture and circulation
enough to carry off the vapor thus secured, and the
quickest and most economical means to these ends may
be used. While on the other hand, in drying wood, whether
in the form of standard stock or the finished product, the
application of the requisite heat and circulation must be
carefully regulated throughout the entire process, or
warping and checking are almost certain to result. Moreover,
wood of different shapes and thicknesses is very differently
effected by the same treatment. Finally, the
tissues composing the wood, which vary in form and physical
properties, and which cross each other in regular directions,
exert their own peculiar influences upon its behavior
during drying. With our native woods, for instance,
summer-wood and spring-wood show distinct tendencies
in drying, and the same is true in a less degree of heartwood,
as contrasted with sapwood. Or, again, pronounced
medullary rays further complicate the drying problem.

Physical Properties that influence Drying

The principal properties which render the drying of
wood peculiarly difficult are: (1) The irregular shrinkage;
(2) the different ways in which water is contained; (3) the
manner in which moisture transfuses through the wood
from the center to the surface; (4) the plasticity of the
wood substance while moist and hot; (5) the changes
which take place in the hygroscopic and chemical nature
of the surface; and (6) the difference produced in the total
shrinkage by different rates of drying.

The shrinkage is unequal in different directions and
in different portions of the same piece. It is greatest in[126]
the circumferential direction of the tree, being generally
twice as great in this direction as in the radial direction.
In the longitudinal direction, for most woods, it is almost
negligible, being from 20 to over 100 times as great circumferentially
as longitudinally.

There is a great variation in different species in this
respect. Consequently, it follows from necessity that
large internal strains are set up when the wood shrinks,
and were it not for its plasticity it would rupture. There
is an enormous difference in the total amount of shrinkage
of different species of wood, varying from a shrinkage of
only 7 per cent in volume, based on the green dimensions,
in the case of some of the cedars to nearly 50 per cent in
the case of some species of eucalyptus.

When the free water in the capillary spaces of the wood
fibre is evaporated it follows the laws of evaporation from
capillary spaces, except that the passages are not all free
passages, and much of the water has to pass out by a
process of transfusion through the moist cell walls. These
cell walls in the green wood completely surround the cell
cavities so that there are no openings large enough to offer
a passage to water or air.

The well-known “pits” in the cell walls extend through
the secondary thickening only, and not through the primary
walls. This statement applies to the tracheids and
parenchyma cells in the conifer (gymnosperms), and to the
tracheids, parenchyma cells, and the wood fibres in the
broad-leaved trees (angiosperms); the vessels in the latter,
however, form open passages except when clogged by
ingrowth called tyloses, and the resin canals in the former
sometimes form occasional openings.

By heating the wood above the boiling point, corresponding
to the external pressure, the free water passes through
the cell walls more readily.

To remove the moisture from the wood substance requires
heat in addition to the latent heat of evaporation,
because the molecules of moisture are so intimately associated
with the molecules, minute particles composing
the wood, that energy is required to separate them therefrom.[127]

Carefully conducted experiments show this to be from
16.6 to 19.6 calories per grain of dry wood in the case of
beech, long-leaf pine, and sugar maple.

The difficulty imposed in drying, however, is not so
much the additional heat required as it is in the rate at
which the water transfuses through the solid wood.

SECTION VIII[128]

ADVANTAGES IN SEASONING

Three most important advantages of seasoning have
already been made apparent:

Freight charges vary considerably in different parts of
the country; but a decrease of 35 to 40 per cent in weight
is important enough to deserve everywhere serious consideration
from those in charge of timber operations.

When timber is shipped long distances over several
roads, as is coming to be more and more the case, the saving
in freight will make a material difference in the cost
of lumber operations, irrespective of any other advantages
of seasoning.[129]

Prevention of Checking and Splitting

Under present methods much timber is rendered unfit
for use by improper seasoning. Green timber, particularly
when cut during January, February, and March,
when the roots are most active, contains a large amount
of water. When exposed to the sun and wind or to high
temperatures in a drying room, the water will evaporate
more rapidly from the outer than from the inner parts
of the piece, and more rapidly from the ends than from
the sides. As the water evaporates, the wood shrinks,
and when the shrinkage is not fairly uniform the wood
cracks and splits.

When wet wood is piled in the sun, evaporation goes
on with such unevenness that the timbers split and crack
in some cases so badly as to become useless for the purpose
for which it was intended. Such uneven drying can be
prevented by careful piling, keeping the logs immersed
in a log pond until wanted, or by piling or storing under
an open shed so that the sun cannot get at them.

Experiments have also demonstrated that injury to
stock in the way of checking and splitting always develops
immediately after the stock is taken into the dry
kiln, and is due to the degree of humidity being too low.

The receiving end of the kiln should always be kept
moist, where the stock has not been steamed before being
put into the kiln, as when the air is too dry it tends to
dry the outside of the stock first—which is termed “case-hardening”—and
in so doing shrinks and closes up the
pores. As the material is moved down the kiln (as
in the case of “progressive kilns”), it absorbs a
continually increasing amount of heat, which tends
to drive off the moisture still present in the center of
the piece, the pores on the outside having been closed
up, there is no exit for the vapor or steam that is being
rapidly formed in the center of the piece. It must find
its way out in some manner, and in doing so sets up strains,
which result either in checking or splitting. If the humidity
had been kept higher, the outside of the piece would
not have dried so quickly, and the pores would have remained[130]
open for the exit of the moisture from the interior
of the piece, and this trouble would have been
avoided. (See also article following.)

Shrinkage of Wood

Since in all our woods, cells with thick walls and cells
with thin walls are more or less intermixed, and especially
as the spring-wood and summer-wood nearly always differ
from each other in this respect, strains and tendencies
to warp are always active when wood dries out, because
the summer-wood shrinks more than the spring-wood,
and heavier wood in general shrinks more than light wood
of the same kind.

If a thin piece of wood after drying is placed upon a
moist surface, the cells on the under side of the piece take
up moisture and swell before the upper cells receive any
moisture. This causes the under side of the piece to become
longer than the upper side, and as a consequence
warping occurs. Soon, however, the moisture penetrates
to all the cells and the piece straightens out. But while
a thin board of pine curves laterally it remains quite
straight lengthwise, since in this direction both shrinkage
and swelling are small. If one side of a green board is
exposed to the sun, warping is produced by the removal of
water and consequent shrinkage of the side exposed; this
may be eliminated by the frequent turning of the topmost
pieces of the piles in order that they may be dried evenly.

As already stated, wood loses water faster from the
ends than from the longitudinal faces. Hence the ends
shrink at a different rate from the interior parts. The
faster the drying at the surface, the greater is the difference
in the moisture of the different parts, and hence the greater
the strains and consequently also the greater amount of
checking. This becomes very evident when freshly cut
wood is placed in the sun, and still more when put into a
hot, dry kiln. While most of these smaller checks are only
temporary, closing up again, some large radial checks remain
and even grow larger as drying progresses. Their
cause is a different one and will presently be explained.
The temporary checks not only appear at the ends, but[131]
are developed on the sides also, only to a much smaller
degree. They become especially annoying on the surface
of thick planks of hardwoods, and also on peeled logs
when exposed to the sun.

So far we have considered the wood as if made up only
of parallel fibres all placed longitudinally in the log.
This, however, is not the case. A large part of the wood
is formed by the medullary or pith rays. In pine over
15,000 of these occur on a square inch of a tangential
section, and even in oak the very large rays, which are
readily visible to the eye, represent scarcely a hundredth
part of the number which a microscope reveals, as the
cells of these rays have their length at right angles to the
direction of the wood fibres.

If a large pith ray of white oak is whittled out and allowed
to dry, it is found to shrink greatly in its width,
while, as we have stated, the fibres to which the ray is
firmly grown in the wood do not shrink in the same direction.
Therefore, in the wood, as the cells of the pith ray
dry they pull on the longitudinal fibres and try to shorten
them, and, being opposed by the rigidity of the fibres, the
pith ray is greatly strained. But this is not the only
strain it has to bear. Since the fibres shrink as much
again as the pith ray, in this its longitudinal direction,
the fibres tend to shorten the ray, and the latter in opposing
this prevents the former from shrinking as much
as they otherwise would.

Thus the structure is subjected to two severe strains
at right angles to each other, and herein lies the greatest
difficulty of wood seasoning, for whenever the wood dries
rapidly these fibres have not the chance to “give” or accommodate
themselves, and hence fibres and pith rays
separate and checking results, which, whether visible or
not, are detrimental in the use of the wood.

The contraction of the pith rays parallel to the length
of the board is probably one of the causes of the small
amount of longitudinal shrinkage which has been observed
in boards. This smaller shrinkage of the pith
rays along the radius of the log (the length of the pith ray),
opposing the shrinkage of the fibres in this direction, becomes[132]
one of the causes of the second great trouble in
wood seasoning, namely, the difference in the shrinkage
along the radius and that along the rings or tangent. This
greater tangential shrinkage appears to be due in part to
the causes just mentioned, but also to the fact that the
greatly shrinking bands of summer-wood are interrupted
along the radius by as many bands of porous spring-wood,
while they are continuous in the tangential direction. In
this direction, therefore, each such band tends to shrink,
as if the entire piece were composed of summer-wood,
and since the summer-wood represents the greater part
of the wood substance, this greater tendency to tangential
shrinkage prevails.

The effect of this greater tangential shrinkage effects
every phase of woodworking. It leads to permanent
checks and causes the log or piece to split open on drying.
Sawed in two, the flat sides of the log become convex;
sawed into timber, it checks along the median line of
the four faces, and if converted into boards, the latter
checks considerably from the end through the center, all
owing to the greater tangential shrinkage of the wood.

Briefly, then, shrinkage of wood is due to the fact that
the cell walls grow thinner on drying. The thicker cell
walls and therefore the heavier wood shrinks most, while
the water in the cell cavities does not influence the volume
of the wood.

Owing to the great difference of cells in shape, size, and
thickness of walls, and still more in their arrangement,
shrinkage is not uniform in any kind of wood. This
irregularity produces strains, which grow with the difference
between adjoining cells and are greatest at the
pith rays. These strains cause warping and checking,
but exist even where no outward signs are visible. They
are greater if the wood is dried rapidly than if dried slowly,
but can never be entirely avoided.

Temporary checks are caused by the more rapid drying
of the outer parts of any stick; permanent checks
are due to the greater shrinkage, tangentially, along the
rings than along the radius. This, too, is the cause of
most of the ordinary phenomena of shrinkage, such as[133]
the difference in behavior of the entire and quartered logs,
“bastard” (tangent) and rift (radial) boards, etc., and
explains many of the phenomena erroneously attributed
to the influence of bark, or of the greater shrinkage of
outer and inner parts of any log.

Once dry, wood may be swelled again to its original
size by soaking in water, boiling, or steaming. Soaked
pieces on drying shrink again as before; boiled and steamed
pieces do the same, but to a slightly less degree. Neither
hygroscopicity, i.e., the capacity of taking up water, nor
shrinkage of wood can be overcome by drying at temperatures
below 200 degrees Fahrenheit. Higher temperatures,
however, reduce these qualities, but nothing short of a
coaling heat robs wood of the capacity to shrink and swell.

Rapidly dried in a kiln, the wood of oak and other
hardwoods “case-harden,” that is, the outer part dries
and shrinks before the interior has a chance to do the same,
and thus forms a firm shell or case of shrunken, commonly
checked wood around the interior. This shell does not
prevent the interior from drying, but when this drying
occurs the interior is commonly checked along the medullary
rays, commonly called “honeycombing” or “hollow-horning.”
In practice this occurrence can be prevented
by steaming or sweating the wood in the kiln, and still
better by drying the wood in the open air or in a shed
before placing in the kiln. Since only the first shrinkage
is apt to check the wood, any kind of lumber which has
once been air-dried (three to six months for one-inch stuff)
may be subjected to kiln heat without any danger from
this source.

Kept in a bent or warped condition during the first
shrinkage, the wood retains the shape to which it has
been bent and firmly opposes any attempt at subsequent
straightening.

Sapwood, as a rule, shrinks more than heartwood of
the same weight, but very heavy heartwood may shrink
more than lighter sapwood. The amount of water in
wood is no criterion of its shrinkage, since in wet wood
most of the water is held in the cavities, where it has no
effect on the volume.[134]

The wood of pine, spruce, cypress, etc., with its very
regular structure, dries and shrinks evenly, and suffers
much less in seasoning than the wood of broad-leaved
(hardwood) trees. Among the latter, oak is the most
difficult to dry without injury.

Desiccating the air with certain chemicals will cause the
wood to dry, but wood thus dried at 80 degrees Fahrenheit
will still lose water in the kiln. Wood dried at 120 degrees
Fahrenheit loses water still if dried at 200 degrees Fahrenheit,
and this again will lose more water if the temperature
be raised, so that absolutely dry wood cannot be obtained,
and chemical destruction sets in before all the water is
driven off.

On removal from the kiln, the dry wood at once takes
up moisture from the air, even in the driest weather. At
first the absorption is quite rapid; at the end of a week
a short piece of pine, 11⁄2 inches thick, has regained two
thirds of, and, in a few months, all the moisture which it
had when air-dry, 8 to 10 per cent, and also its former
dimensions. In thin boards all parts soon attain the
same degree of dryness. In heavy timbers the interior remains
more moist for many months, and even years, than
the exterior parts. Finally an equilibrium is reached,
and then only the outer parts change with the weather.

With kiln-dried woods all parts are equally dry, and
when exposed, the moisture coming from the air must
pass through the outer parts, and thus the order is reversed.
Ordinary timber requires months before it is
at its best. Kiln-dried timber, if properly handled, is
prime at once.

Dry wood if soaked in water soon regains its original
volume, and in the heartwood portion it may even surpass
it; that is to say, swell to a larger dimension than
it had when green. With the soaking it continues to
increase in weight, the cell cavities filling with water, and
if left many months all pieces sink. Yet after a year’s
immersion a piece of oak 2 by 2 inches and only 6 inches
long still contains air; i.e., it has not taken up all the
water it can. By rafting or prolonged immersion, wood
loses some of its weight, soluble materials being leached[135]
out, but it is not impaired either as fuel or as building
material. Immersion, and still more boiling and steaming,
reduce the hygroscopicity of wood and therefore also
the troublesome “working,” or shrinking and swelling.

Exposure in dry air to a temperature of 300 degrees Fahrenheit
for a short time reduces but does not destroy the
hygroscopicity, and with it the tendency to shrink and
swell. A piece of red oak which has been subjected to a
temperature of over 300 degrees Fahrenheit still swells in
hot water and shrinks in a dry kiln.

Expansion of Wood

It must not be forgotten that timber, in common with
every other material, expands as well as contracts. If
we extract the moisture from a piece of wood and so cause
it to shrink, it may be swelled to its original volume by
soaking it in water, but owing to the protection given to
most timber in dwelling-houses it is not much affected by
wet or damp weather. The shrinkage is more apparent,
more lasting, and of more consequence to the architect,
builder, or owner than the slight expansion which takes
place, as, although the amount of moisture contained in
wood varies with the climate conditions, the consequence
of dampness or moisture on good timber used in houses
only makes itself apparent by the occasional jamming of a
door or window in wet or damp weather.

Considerable expansion, however, takes place in the
wood-paving of streets, and when this form of paving
was in its infancy much trouble occurred owing to all
allowances not having been made for this contingency,
the trouble being doubtless increased owing to the blocks
not being properly seasoned; curbing was lifted or pushed
out of line and gully grids were broken by this action. As
a rule in street paving a space of one or two inches wide
is now left next to the curb, which is filled with sand or
some soft material, so that the blocks may expand longitudinally
without injuring the contour or affecting the curbs.
But even with this arrangement it is not at all unusual
for an inch or more to have to be cut off paving blocks
parallel to the channels some time after the paving has[136]
been laid, owing to the expansion of the wood exceeding
the amounts allowed.

Considerable variation occurs in the expansion of wood
blocks, and it is noticeable in the hardwoods as well as in
the softwoods, and is often greater in the former than in
the latter.

Expansion takes place in the direction of the length of
the blocks as they are laid across the street, and causes
no trouble in the other direction, the reason being that
the lengthway of a block of wood is across the grain, of
the timber, and it expands or contracts as a plank does.
On one occasion, in a roadway forty feet wide, expansion
occurred until it amounted to four inches on each side,
or eight inches in all. This continual expansion and contraction
is doubtless the cause of a considerable amount of
wood street-paving bulging and becoming filled with
ridges and depressions.

Elimination of Stain and Mildew

A great many manufacturers, and particularly those
located in the Southern States, experience a great amount
of difficulty in their timber becoming stained and mildewed.
This is particularly true with gum wood, as it will
frequently stain and mould in twenty-four hours, and
they have experienced so much of this trouble that they
have, in a great many instances, discontinued cutting it
during the summer season.

If this matter were given proper attention they should
be able to eliminate a great deal of this difficulty, as no
doubt they will find after investigation that the mould
has been caused by the stock being improperly piled to
the weather.

Freshly sawn wood, placed in close piles during warm,
damp weather in the months of July and August, presents
especially favorable conditions for mould and stain. In
all cases it is the moist condition and retarded drying of
the wood which causes this. Therefore, any method which
will provide for the rapid drying of the wood before or
after piling will tend to prevent the difficulty, and the
best method for eliminating mould is (1) to provide for[137]
as little delay as possible between the felling of the tree,
and its manufacture into rough products before the sap
has had an opportunity of becoming sour. This is especially
necessary with trees felled from April to September,
in the region north of the Gulf States, and from March
to November in the latter, while the late fall and winter
cutting should all be worked up by March or April. (2)
The material should be piled to the weather immediately
after being sawn or cut, and every precaution should be
taken in piling to facilitate rapid drying, by keeping the
piles or ricks up off the ground. (3) All weeds (and emphasis
should be placed on the ALL) and other vegetation
should be kept well clear of the piles, in order that the
air may have a clear and unobstructed passage through and
around the piles, and (4) the piles should be so constructed
that each stick or piece will have as much air space about
it as it is possible to give to it.

If the above instructions are properly carried out, there
will be little or no difficulty experienced with mould appearing
on the lumber.

SECTION IX[138]

DIFFICULTIES OF DRYING
WOOD

Seasoning and kiln-drying is so important a process in
the manufacture of woods that a need is keenly felt for
fuller information regarding it, based upon scientific study
of the behavior of various species at different mechanical
temperatures and under different mechanical drying processes.
The special precautions necessary to prevent loss
of strength or distortion of shape render the drying of
wood especially difficult.

All wood when undergoing a seasoning process, either
natural (by air) or mechanical (by steam or heat in a dry
kiln), checks or splits more or less. This is due to the
uneven drying-out of the wood and the consequent strains
exerted in opposite directions by the wood fibres in shrinking.
This shrinkage, it has been proven, takes place both
end-wise and across the grain of the wood. The old tradition
that wood does not shrink end-wise has long since
been shattered, and it has long been demonstrated that
there is an end-wise shrinkage.

In some woods it is very light, while in others it is easily
perceptible. It is claimed that the average end shrinkage,
taking all the woods, is only about 11⁄2 per cent. This,
however, probably has relation to the average shrinkage
on ordinary lumber as it is used and cut and dried. Now
if we depart from this and take veneer, or basket stock,
or even stave bolts where they are boiled, causing swelling
both end-wise and across the grain or in dimension, after
they are thoroughly dried, there is considerably more
evidence of end shrinkage. In other words, a slack barrel
stave of elm, say, 28 or 30 inches in length, after being[139]
boiled might shrink as much in thoroughly drying-out
as compared to its length when freshly cut, as a 12-foot
elm board.

It is in cutting veneer that this end shrinkage becomes
most readily apparent. In trimming with scoring knives
it is done to exact measure, and where stock is cut to fit
some specific place there has been observed a shrinkage
on some of the softer woods, like cottonwood, amounting
to fully 1⁄8 of an inch in 36 inches. And at times where
drying has been thorough the writer has noted a shrinkage
of 1⁄8 of an inch on an ordinary elm cabbage-crate strip
36 inches long, sawed from the log without boiling.

There are really no fixed rules of measurement or allowance,
however, because the same piece of wood may
vary under different conditions, and, again, the grain
may cross a little or wind around the tree, and this of
itself has a decided effect on the amount of what is termed
“end shrinkage.”

There is more checking in the wood of the broad-leaf
(hardwood) trees than in that of the coniferous (softwood)
trees, more in sapwood than in heartwood, and more in
summer-wood than in spring-wood.

Inasmuch as under normal conditions of weather, water
evaporates less rapidly during the early seasoning of
winter, wood that is cut in the autumn and early winter
is considered less subject to checking than that which is
cut in spring and summer.

Rapid seasoning, except after wood has been thoroughly
soaked or steamed, almost invariably results in more or
less serious checking. All hardwoods which check or
warp badly during the seasoning should be reduced to
the smallest practicable size before drying to avoid the
injuries involved in this process, and wood once seasoned
should never again be exposed to the weather, since all injuries
due to seasoning are thereby aggravated.

Seasoning increases the strength of wood in every respect,
and it is therefore of great importance to protect
the wood against moisture.[140]

Changes rendering Drying difficult

An important property rendering drying of wood peculiarly
difficult is the changes which occur in the hygroscopic
properties of the surface of a stick, and the rate
at which it will allow moisture to pass through it. If
wood is dried rapidly the surface soon reaches a condition
where the transfusion is greatly hindered and sometimes
appears almost to cease. The nature of this action is
not well understood and it differs greatly in different species.
Bald cypress (Taxodium distichum) is an example in which
this property is particularly troublesome. The difficulty
can be overcome by regulating the humidity during the
drying operation. It is one of the factors entering into
production of what is called “case-hardening” of wood,
where the surface of the piece becomes hardened in a
stretched or expanded condition, and subsequent shrinkage
of the interior causes “honeycombing,” “hollow-horning,”
or internal checking. The outer surface of
the wood appears to undergo a chemical change in the
nature of hydrolization or oxidization, which alters the
rate of absorption and evaporation in the air.

As the total amount of shrinkage varies with the rate
at which the wood is dried, it follows that the outer surface
of a rapidly dried board shrinks less than the interior.
This sets up an internal stress, which, if the board be
afterward resawed into two thinner boards by slicing it
through the middle, causes the two halves to cup with
their convex surfaces outward. This effect may occur
even though the moisture distribution in the board has
reached a uniform condition, and the board is thoroughly
dry before it is resawed. It is distinct from the well-known
“case-hardening” effect spoken of above, which
is caused by unequal moisture conditions.

The manner in which the water passes from the interior
of a piece of wood to its surface has not as yet been
fully determined, although it is one of the most important
factors which influence drying. This must involve a
transfusion of moisture through the cell walls, since, as
already mentioned, except for the open vessels in the hardwoods,[141]
free resin ducts in the softwoods, and possibly the
intercellular spaces, the cells of green wood are enclosed
by membranes and the water must pass through the walls
or the membranes of the pits. Heat appears to increase
this transfusion, but experimental data are lacking.

It is evident that to dry wood properly a great many
factors must be taken into consideration aside from the
mere evaporation of moisture.

Losses Due to Improper Kiln-drying

In some cases there is practically no loss in drying, but
more often it ranges from 1 to 3 per cent, and 7 to 10 per
cent in refractory woods such as gum. In exceptional
instances the losses are as high as 33 per cent.

In air-drying there is little or no control over the process;
it may take place too rapidly on some days and too
slowly on others, and it may be very non-uniform.

Hardwoods in large sizes almost invariably check.

By proper kiln-drying these unfavorable circumstances
may be eliminated. However, air-drying is unquestionably
to be preferred to bad kiln-drying, and when there
is any doubt in the case it is generally safer to trust to
air-drying.

If the fundamental principles are all taken care of, green
lumber can be better dried in the dry kiln.

Properties of Wood that affect Drying

It is clear, from the previous discussion of the structure
of wood, that this property is of first importance among
those influencing the seasoning of wood. The free water
way usually be extracted quite readily from porous hardwoods.
The presence of tyloses in white oak makes even
this a difficult problem. On the other hand, its more
complex structure usually renders the hygroscopic moisture
quite difficult to extract.

The lack of an open, porous structure renders the transfusion
of moisture through some woods very slow, while
the reverse may be true of other species. The point of
interest is that all the different variations in structure[142]
affect the drying rates of woods. The structure of the
gums suggests relatively easy seasoning.

Shrinkage is a very important factor affecting the drying
of woods. Generally speaking, the greater the shrinkage
the more difficult it is to dry wood. Wood shrinks
about twice as much tangentially as radially, thus introducing
very serious stresses which may cause loss in woods
whose total shrinkage is large. It has been found that
the amount of shrinkage depends, to some extent, on the
rate and temperature at which woods season. Rapid
drying at high or low temperature results in slight shrinkage,
while slow drying, especially at high temperature,
increases the shrinkage.

As some woods must be dried in one way and others in
other ways, to obtain the best general results, this effect
may be for the best in one case and the reverse in others.
As an example one might cite the case of Southern white
oak. This species must be dried very slowly at low temperatures
in order to avoid the many evils to which it is
heir. It is interesting to note that this method tends to
increase the shrinkage, so that one might logically expect
such treatment merely to aggravate the evils. Such
is not the case, however, as too fast drying results in other
defects much worse than that of excessive shrinkage.

Thus we see that the shrinkage of any given species of
wood depends to a great extent on the method of drying.
Just how much the shrinkage of gum is affected by the
temperature and drying rate is not known at present.
There is no doubt that the method of seasoning affects
the shrinkage of the gums, however. It is just possible
that these woods may shrink longitudinally more than
is normal, thus furnishing another cause for their peculiar
action under certain circumstances. It has been found
that the properties of wood which affect the seasoning of
the gums are, in the order of their importance: (1) The
indeterminate and erratic grain; (2) the uneven shrinkage
with the resultant opposing stresses; (3) the plasticity
under high temperature while moist; and (4) the slight
apparent lack of cohesion between the fibres. The first,
second, and fourth properties are clearly detrimental,[143]
while the third may possibly be an advantage in reducing
checking and “case-hardening.”

The grain of the wood is a prominent factor also affecting
the problem. It is this factor, coupled with uneven
shrinkage, which is probably responsible, to a large extent,
for the action of the gums in drying. The grain may be
said to be more or less indeterminate. It is usually spiral,
and the spiral may reverse from year to year of the tree’s
growth. When a board in which this condition exists
begins to shrink, the result is the development of opposing
stresses, the effect of which is sometimes disastrous. The
shrinkage around the knots seems to be particularly uneven,
so that checking at the knots is quite common.

Some woods, such as Western red cedar, redwood, and
eucalyptus, become very plastic when hot and moist.
The result of drying-out the free water at high temperature
may be to collapse the cells. The gums are known
to be quite soft and plastic, if they are moist, at high
temperature, but they do not collapse so far as we have
been able to determine.

The cells of certain species of wood appear to lack
cohesion, especially at the junction between the annual
rings. As a result, checks and ring shakes are very common
in Western larch and hemlock. The parenchyma
cells of the medullary rays in oak do not cohere strongly
and often check open, especially when steamed too severely.

Unsolved Problems in Kiln-drying

These questions can be answered thus far only by speculation
or, at best, on the basis of incomplete data.

Until these problems are solved, kiln-drying must
necessarily remain without the guidance of complete
scientific theory.

A correct understanding of the principles of drying is
rare, and opinions in regard to the subject are very diverse.
The same lack of knowledge exists in regard to dry kilns.
The physical properties of the wood which complicate
the drying operation and render it distinct from that of
merely evaporating free water from some substance like
a piece of cloth must be studied experimentally. It cannot
well be worked out theoretically.

SECTION X[145]

HOW WOOD IS SEASONED

Methods of Drying

The choice of a method of drying depends largely upon
the object in view. The principal objects may be grouped
under three main heads, as follows:

• 1. To reduce shipping weight.
• 2. To reduce the quantity necessary to carry in stock.
• 3. To prepare the wood for its ultimate use and improve
  its qualities.

When wood will stand the temperature without excessive
checking or undue shrinkage or loss in strength,
the first object is most readily attained by heating the
wood above the boiling point in a closed chamber, with
a large circulation of air or vapor, so arranged that the
excess steam produced will escape. This process manifestly
does not apply to many of the hardwoods, but is
applicable to many of the softwoods. It is used especially
in the northwestern part of the United States, where
Douglas fir boards one inch thick are dried in from 40 to
65 hours, and sometimes in as short a time as 24 hours.
In the latter case superheated steam at 300 degrees Fahrenheit
was forced into the chamber but, of course, the
lumber could not be heated thereby much above the boiling
point so long as it contained any free water.

This lumber, however, contained but 34 per cent moisture
to start with, and the most rapid rate was 1.6 per cent
loss per hour.

The heat of evaporation may be supplied either by
superheated steam or by steam pipes within the kiln
itself.

The quantity of wood it is necessary to carry in stock[146]
is naturally reduced when either of the other two objects
is attained and, therefore, need not necessarily be discussed.

In drying to prepare for use and to improve quality,
careful and scientific drying is called for. This applies
more particularly to the hardwoods, although it may be
required for softwoods also.

Drying at Atmospheric Pressure

Present practice of kiln-drying varies tremendously
and there is no uniformity or standard method.

Temperatures vary anywhere from 65 to 165 degrees
Fahrenheit, or even higher, and inch boards three to six
months on the sticks are being dried in from four days to
three weeks, and three-inch material in from two to five
months.

All methods in use at atmospheric pressure may be
classified under the following headings. The kilns may
be either progressive or compartment, and preliminary
steaming may or may not be used with any one of these
methods:

• 1. Dry air heated. This is generally obsolete.
• 2. Moist air.
• • a. Ventilated.
  • b. Forced draft.
  • c. Condensing.
  • d. Humidity regulated.
  • e. Boiling.
• 3. Superheated steam.

Drying under Pressure and Vacuum

Various methods of drying wood under pressures other
than atmospheric have been tried. Only a brief mention
of this subject will be made. Where the apparatus is
available probably the quickest way to dry wood is first
to heat it in saturated steam at as high a temperature
as the species can endure without serious chemical change
until the heat has penetrated to the center, then follow
this with a vacuum.[147]

By this means the self-contained specific heat of the
wood and the water is made available for the evaporation,
and the drying takes place from the inside outwardly,
just the reverse of that which occurs by drying by means
of external heat.

When the specimen has cooled this process is then to be
repeated until it has dried down to fibre-saturation point.
It cannot be dried much below this point by this method,
since the absorption during the heating operation will
then equal the evaporation during the cooling. It may
be carried further, however, by heating in partially humidified
air, proportioning the relative humidity each
time it is heated to the degree of moisture present in the
wood.

The point to be considered in this operation is that
during the heating process no evaporation shall be allowed
to take place, but only during the cooling. In this way
surface drying and “case-hardening” are prevented since
the heat is from within and the moisture passes from the
inside outwardly. However, with some species, notably
oak, surface cracks appear as a network of fine checks
along the medullary rays.

In the first place, it should be borne in mind that it is
the heat which produces evaporation and not the air nor
any mysterious property assigned to a “vacuum.”

For every pound of water evaporated at ordinary temperatures
approximately 1,000 British thermal units of
heat are used up, or “become latent,” as it is called. This
is true whether the evaporation takes place in a vacuum
or under a moderate air pressure. If this heat is not supplied
from an outside source it must be supplied by the
water itself (or the material being dried), the temperature
of which will consequently fall until the surrounding
space becomes saturated with vapor at a pressure corresponding
to the temperature which the water has reached;
evaporation will then cease. The pressure of the vapor
in a space saturated with water vapor increases rapidly
with increase of temperature. At a so-called vacuum of
28 inches, which is about the limit in commercial operations,
and in reality signifies an actual pressure of 2 inches[148]
of mercury column, the space will be saturated with vapor
at 101 degrees Fahrenheit. Consequently, no evaporation
will take place in such a vacuum unless the water be
warmer than 101 degrees Fahrenheit, provided there is
no air leakage. The qualification in regard to air is necessary,
for the sake of exactness, for the following reason:
In any given space the total actual pressure is made up
of the combined pressures of all the gases present. If the
total pressure (“vacuum”) is 2 inches, and there is no air
present, it is all produced by the water vapor (which
saturates the space at 101 degrees Fahrenheit); but if
some air is present and the total pressure is still maintained
at 2 inches, then there must be less vapor present, since
the air is producing part of the pressure and the space is
no longer saturated at the given temperature. Consequently
further evaporation may occur, with a corresponding
lowering of the temperature of the water, until a balance
is again reached. Without further explanation it is easy
to see that but little water can be evaporated by a vacuum
alone without addition of heat, and that the prevalent
idea that a vacuum can of itself produce evaporation is
a fallacy. If heat be supplied to the water, however,
either by conduction or radiation, evaporation will take
place in direct proportion to the amount of heat supplied,
so long as the pressure is kept down by the vacuum
pump.

At 30 inches of mercury pressure (one atmosphere) the
space becomes saturated with vapor and equilibrium is
established at 212 degrees Fahrenheit. If heat be now
supplied to the water, however, evaporation will take
place in proportion to the amount of heat supplied, so
long as the pressure remains that of one atmosphere, just
as in the case of the vacuum. Evaporation in this condition,
where the vapor pressure at the temperature of
the water is equal to the gas pressure on the water,
is commonly called “boiling,” and the saturated vapor
entirely displaces the air under continuous operation.
Whenever the space is not saturated with vapor, whether
air is present or not, evaporation will take place, by boiling
if no air be present or by diffusion under the presence[149]
of air, until an equilibrium between temperature and
vapor pressure is resumed.

Relative humidity is simply the ratio of the actual vapor
pressure present in a given space to the vapor pressure
when the space is saturated with vapor at the given temperature.
It matters not whether air be present or not.
One hundred per cent humidity means that the space
contains all the vapor which it can hold at the given
temperature—it is saturated. Thus at 100 per cent
humidity and 212 degrees Fahrenheit the space is saturated,
and since the pressure of saturated vapor at this
temperature is one atmosphere, no air can be present
under these conditions. If, however, the total pressure
at this temperature were 20 pounds (5 pounds gauge),
then it would mean that there was 5 pounds air pressure
present in addition to the vapor, yet the space would still
be saturated at the given temperature. Again, if the
temperature were 101 degrees Fahrenheit, the pressure
of saturated vapor would be only 1 pound, and the additional
pressure of 14 pounds, if the total pressure were
atmospheric, would be made up of air. In order to have
no air present and the space still saturated at 101 degrees
Fahrenheit, the total pressure must be reduced to 1 pound
by a vacuum pump. Fifty per cent relative humidity,
therefore, signifies that only half the amount of vapor
required to saturate the space at the given temperature
is present. Thus at 212 degrees Fahrenheit temperature
the vapor pressure would only be 71⁄2pounds (vacuum of
15 inches gauge). If the total pressure were atmospheric,
then the additional 71⁄2 pounds would be simply air.

“Live steam” is simply water-saturated vapor at a
pressure usually above atmospheric. We may just as
truly have live steam at pressures less than atmospheric,
at a vacuum of 28 inches for instance. Only in the latter
case its temperature would be lower, viz., 101 degrees
Fahrenheit.

Superheated steam is nothing more than water vapor
at a relative humidity less than saturation, but is usually
considered at pressures above atmospheric, and in the
absence of air. The atmosphere at, say, 50 per cent relative[150]
humidity really contains superheated steam or vapor,
the only difference being that it is at a lower temperature
and pressure than we are accustomed to think of in speaking
of superheated steam, and it has air mixed with it to
make up the deficiency in pressure below the atmosphere.

Two things should now be clear; that evaporation is
produced by heat and that the presence or absence of air
does not influence the amount of evaporation. It does,
however, influence the rate of evaporation, which is retarded
by the presence of air. The main things influencing
evaporation are, first, the quantity of heat supplied
and, second, the relative humidity of the immediately
surrounding space.

Drying by Superheated Steam

What this term really signifies is simply water vapor
in the absence of air in a condition of less than saturation.
Kilns of this type are, properly speaking, vapor kilns,
and usually operate at atmospheric pressure, but may be
used at greater pressures or at less pressures. As stated
before, the vapor present in the air at any humidity less
than saturation is really “superheated steam,” only at a
lower pressure than is ordinarily understood by this term,
and mixed with air. The main argument in favor of this
process seems to be based on the idea that steam is moist
heat. This is true, however, only when the steam is near
saturation. When it is superheated it is just as dry as
air containing the same relative humidity. For instance,
steam at atmospheric pressure and heated to 248 degrees
Fahrenheit has a relative humidity of only 50 per cent and
is just as dry as air containing the same humidity. If
heated to 306 degrees Fahrenheit, its relative humidity
is reduced to 20 per cent; that is to say, the ratio of its
actual vapor pressure (one atmosphere) to the pressure
of saturated vapor at this temperature (five atmospheres)
is 1:5, or 20 per cent. Superheated vapor in the absence
of air, however, parts with its heat with great rapidity
and finally becomes saturated when it has lost all of its
ability to cause evaporation. In this respect it is more
moist than air when it comes in contact with bodies which[151]
are at a lower temperature. When saturated steam is
used to heat the lumber it can raise the temperature of
the latter to its own temperature, but cannot produce
evaporation unless, indeed, the pressure is varied. Only
by the heat supplied above the temperature of saturation
can evaporation be produced.

Impregnation Methods

Methods of partially overcoming the shrinkage by impregnation
of the cell walls with organic materials closely
allied to the wood substance itself are in use. In one of
these which has been patented, sugar is used as the impregnating
material, which is subsequently hardened or
“caramelized” by heating. Experiments which the United
States Forest Service has made substantiate the claims
that the sugar does greatly reduce the shrinkage of the
wood; but the use of impregnation processes is determined
rather from a financial economic standpoint than by the
physical result obtained.

Another process consists in passing a current of electricity
through the wet boards or through the green logs
before sawing. It is said that the ligno cellulose and the
sap are thus transformed by electrolysis, and that the
wood subsequently dries more rapidly.

Preliminary Treatments

In many dry kiln operations, especially where the kilns
are not designed for treatments with very moist air, the
wood is allowed to air-season from several months to a
year or more before running it into the dry kiln. In this
way the surface dries below its fibre-saturation point and
becomes hardened or “set” and the subsequent shrinkage
is not so great. Moreover, there is less danger of
surface checking in the kiln, since the surface has already
passed the danger point. Many woods, however, check
severely in air-drying or case-harden in the air. It is
thought that such woods can be satisfactorily handled in
a humidity-regulated kiln direct from the saw.

Preliminary steaming is frequently used to moisten the
surface if case-hardened, and to heat the lumber through[152]
to the center before drying begins. This is sometimes
done in a separate chamber, but more often in a compartment
of the kiln itself, partitioned off by means of a
curtain which can be raised or lowered as circumstances
require. This steaming is usually conducted at atmospheric
pressure and frequently condensed steam is used
at temperatures far below 212 degrees Fahrenheit. In
a humidity-regulated kiln this preliminary treatment may
be omitted, since nearly saturated conditions can be
maintained and graduated as the drying progresses.

Recently the process of steaming at pressures up to
20 pounds gauge in a cylinder for short periods of time,
varying from 5 to 20 minutes, is being advocated in the
United States. The truck load is run into the cylinder,
steamed, and then taken directly out into the air. It
may subsequently be placed in the dry kiln if further drying
is desired. The self-contained heat of the wood evaporates
considerable moisture, and the sudden drying of
the boards causes the shrinkage to be reduced slightly
in some cases. Such short periods of steaming under
20 pounds pressure do not appear to injure the wood
mechanically, although they do darken the color appreciably,
especially of the sapwood of the species having a
light-colored sap, as black walnut (Juglans nigra) and
red gum (Liquidamber styraciflua). Longer periods of
steaming have been found to weaken the wood. There
is a great difference in the effect on different species,
however.

Soaking wood for a long time before drying has been
practised, but experiments indicate that no particularly
beneficial results, from the drying standpoint, are attained
thereby. In fact, in some species containing sugars and
allied substances it is probably detrimental from the
shrinkage standpoint. If soaked in boiling water some
species shrink and warp more than if dried without this
treatment.

In general, it may be said that, except possibly for
short-period steaming as described above, steaming and
soaking hardwoods at temperatures of 212 degrees Fahrenheit
or over should be avoided if possible.[153]

It is the old saying that wood put into water shortly
after it is felled, and left in water for a year or more, will
be perfectly seasoned after a short subsequent exposure
to the air. For this reason rivermen maintain that
timber is made better by rafting. Herzenstein says:
“Floating the timber down rivers helps to wash out the
sap, and hence must be considered as favorable to its
preservation, the more so as it enables it to absorb more
preservative.”

Wood which has been buried in swamps is eagerly
sought after by carpenters and joiners, because it has
lost all tendency to warp and twist. When first taken
from the swamp the long-immersed logs are very much
heavier than water, but they dry with great rapidity.
A cypress log from the Mississippi Delta, which two men
could barely handle at the time it was taken out some
years ago, has dried out so much since then that to-day
one man can lift it with ease. White cedar telegraph
poles are said to remain floating in the water of the Great
Lakes sometimes for several years before they are set in
lines and to last better than freshly cut poles.

It is very probable that immersion for long periods in
water does materially hasten subsequent seasoning. The
tannins, resins, albuminous materials, etc., which are
deposited in the cell walls of the fibres of green wood, and
which prevent rapid evaporation of the water, undergo
changes when under water, probably due to the action of
bacteria which live without air, and in the course of time
many of these substances are leached out of the wood.
The cells thereby become more and more permeable to
water, and when the wood is finally brought into the air
the water escapes very rapidly and very evenly. Herzenstein’s
statement that wood prepared by immersion
and subsequent drying will absorb more preservative,
and that with greater rapidity, is certainly borne out by
experience in the United States.

It is sometimes claimed that all seasoning preparatory
to treatment with a substance like tar oil might be done
away with by putting the green wood into a cylinder with
the oil and heating to 225 degrees Fahrenheit, thus driving[154]
the water off in the form of steam, after which the tar oil
would readily penetrate into the wood. This is the basis
of the so-called “Curtiss process” of timber treatment.
Without going into any discussion of this method of
creosoting, it may be said that the same objection made
for steaming holds here. In order to get a temperature of
212 degrees Fahrenheit in the center of the treated wood,
the outside temperature would have to be raised so high
that the strength of the wood might be seriously injured.

A company on the Pacific coast which treats red fir piling
asserts that it avoids this danger by leaving the green
timber in the tar oil at a temperature which never exceeds
225 degrees Fahrenheit for from five to twelve hours, until
there is no further evidence of water vapor coming out of
the wood. The tar oil is then run out, and a vacuum is
created for about an hour, after which the oil is run in
again and is kept in the cylinders under 100 pounds pressure
for from ten to twelve hours, until the required amount
of absorption has been reached (about 12 pounds per
cubic foot).

Out-of-door Seasoning

The most effective seasoning is without doubt that
obtained by the uniform, slow drying which takes place
in properly constructed piles outdoors, under exposure
to the winds and the sun. Lumber has always been
seasoned in this way, which is still the best for ordinary
purposes.

It is probable for the sake of economy, air-drying will
be eliminated in the drying process of the future without
loss to the quality of the product, but as yet no effective
method has been discovered whereby this may be accomplished,
because nature performs certain functions
in air-drying that cannot be duplicated by artificial means.
Because of this, hardwoods, as a rule, cannot be successfully
kiln-dried green or direct from the saw, and must
receive a certain amount of preliminary air-drying before
being placed in a dry kiln.

The present methods of air-seasoning in use have been
determined by long experience, and are probably as good[155]
as they could be made for present conditions. But the
same care has not up to this time been given to the seasoning
of such timber as ties, bridge material, posts, telegraph
and telephone poles, etc. These have sometimes been
piled more or less intelligently, but in the majority of
cases their value has been too low to make it seem worth
while to pile with reference to anything beyond convenience
in handling.

In piling material for air-seasoning, one should utilize
high, dry ground when possible, and see that the foundations
are high enough off the ground, so that there is
proper air circulation through the bottom of the piles,
and also that the piles are far enough apart so that the
air may circulate freely through and around them.

It is air circulation that is desired in all cases of drying,
both in dry kilns and out-of-doors, and not sunshine; that
is, not the sun shining directly upon the material. The
ends also should be protected from the sun, and everything
possible done to induce a free circulation of air, and
to keep the foundations free from all plant growth.

Naturally, the heavier the material to be dried, the more
difficulty is experienced from checking, which has its most
active time in the spring when the sap is rising. In fact
the main period of danger in material checking comes
with the March winds and the April showers, and not
infrequently in the South it occurs earlier than that. In
other words, as soon as the sap begins to rise, the timber
shows signs of checking, and that is the time to take extra
precautions by careful piling and protection from the sun.
When the hot days of summer arrive the tendency to
check is not so bad, but stock will sour from the heat,
stain from the sap, mildew from moisture, and fall a prey
to wood-destroying insects.

It has been proven in a general way that wood will
season more slowly in winter than in summer, and also
that the water content during various months varies. In
the spring the drying-out of wood cut in October and
November will take place more rapidly.

SECTION XI[156]

KILN-DRYING OF WOOD

Advantages of Kiln-drying over Air-drying

Some of the advantages of kiln-drying to be secured
over air-drying in addition to reducing the shipping weight
and lessening quantity of stock are the following:

• 1. Less material lost.
• 2. Better quality of product.
• 3. Prevention of sap stain and mould.
• 4. Fixation of gums and resins.
• 5. Reduction of hygroscopicity.

This reduction in the tendency to take up moisture
means a reduction in the “working” of the material which,
even though slight, is of importance.

The problem of drying wood in the best manner divides
itself into two distinct parts, one of which is entirely concerned
with the behavior of the wood itself and the physical
phenomena involved, while the other part has to do
with the control of the drying process.

Physical Conditions governing the Drying of Wood

Theory of Kiln-drying

The dry kiln has long since acquired particular appreciation
at the hands of those who have witnessed its
time-saving qualities, when practically applied to the drying
of timber. The science of drying is itself of the simplest,
the exposure to the air being, indeed, the only means
needed where the matter of time is not called into question.
Otherwise, where hours, even minutes, have a marked
significance, then other means must be introduced to
bring about the desired effect. In any event, however,
the same simple and natural remedy pertains,—the
absorption of moisture. This moisture in green timber
is known as “sap”, which is itself composed of a number
of ingredients, most important among which are water,
resin, and albumen.

All dry kilns in existence use heat to season timber;[158]
that is, to drive out that portion of the “sap” which is
volatile.

The heat does not drive out the resin of the pines nor
the albumen of the hardwoods. It is really of no advantage
in this respect. Resin in its hardened state as
produced by heat is only slowly soluble in water and
contains a large proportion of carbon, the most stable
form of matter. Therefore, its retention in the pores of
the wood is a positive advantage.

To produce the ideal effect the drying must commence
at the heart of the piece and work outward, the moisture
being removed from the surface as fast as it exudes from
the pores of the wood. To successfully accomplish this,
adjustments must be available to regulate the temperature,
circulation, and humidity according to the variations
of the atmospheric conditions, the kind and condition
of the material to be dried.

This ideal effect is only attained by the use of a type
of dry kiln in which the surface of the lumber is kept soft,
the pores being left open until all the moisture within has
been volatilized by the heat and carried off by a free circulation
of air. When the moisture has been removed from
the pores, the surface is dried without closing the pores,
resulting in timber that is clean, soft, bright, straight, and
absolutely free from stains, checks, or other imperfections.

Now, no matter how the method of drying may be
applied, it must be remembered that vapor exists in the
atmosphere at all times, its volume being regulated by
the capacity of the temperature absorbed. To kiln-dry
properly, a free current of air must be maintained, of
sufficient volume to carry off this moisture. Now, the
capacity of this air for drying depends entirely upon the
ability of its temperature to absorb or carry off a larger
proportion of moisture than that apportioned by natural
means. Thus, it will be seen, a cubic foot of air at 32
degrees Fahrenheit is capable of absorbing only two grains
of water, while at 160 degrees, it will dispose of ninety
grains. The air, therefore, should be made as dry as
possible and caused to move freely, so as to remove all
moisture from the surface of the wood as soon as it appears.[159]
Thus the heat effects a double purpose, not only increasing
the rate of evaporation, but also the capacity of the
air for absorption. Where these means are applied, which
rely on the heat alone to accomplish this purpose, only that
of the moisture which is volatile succumbs, while the albumen
and resin becoming hardened under the treatment
close up the pores of the wood. This latter result is
oft-times accomplished while moisture yet remains and
which in an enforced effort to escape bursts open the cells
in which it has been confined and creates what is known
as “checks.”

Therefore, taking the above facts into consideration,
the essentials for the successful kiln-drying of wood may
be enumerated as follows:

Requirements in a Satisfactory Dry Kiln

The requirements in a satisfactory dry kiln are:

• 1. Control of humidity at all times.
• 2. Ample air circulation at all points.
• 3. Uniform and proper temperatures.

In order to meet these requirements the United States
Forestry Service has designed a kiln in which the humidity,
temperature, and circulation can be controlled at all times.

Briefly, it consists of a drying chamber with a partition
on either side, making two narrow side chambers open
top and bottom.

The steam pipes are in the usual position underneath
the material to be dried.

At the top of the side chambers is a spray; at the bottom
are gutters and an eliminator or set of baffle plates to
separate the fine mist from the air.

The spray accomplishes two things: It induces an increased
circulation and it regulates the humidity. This is
done by regulating the temperature of the spray water.

The air under the heating coil is saturated at whatever[161]
temperature is required. This temperature is the dew
point of the air after it passes up into the drying chamber
above the coils. Knowing the temperature in the drying
room and the dew point, the relative humidity is thus
determined.

The relative humidity is simply the ratio of the vapor
pressure at the dew point to the pressure of saturated
vapor (see Fig. 30).

Theory and Description of the Forestry Service Kiln

The humidities and temperatures in the piles of lumber
are largely dependent upon the circulation of air within
the kiln. The temperature and humidity within the kiln,
taken alone, are no criterion of the conditions of drying
the pile of lumber if the circulation in any portion[162]
is deficient. It is possible to have an extremely rapid circulation
of air within the dry kiln itself and yet have
stagnation within the individual piles, the air passing
chiefly through open spaces and channels. Wherever
stagnation exists or the movement of air is too sluggish
the temperature will drop and the humidity increase,
perhaps to the point of saturation.

When in large kilns the forced circulation is in the opposite
direction from that induced by the cooling of the
air by the lumber, there is always more or less uncertainty
as to the movement of the air through the piles. Even
with the boards placed edge-wise, with stickers running
vertically, and with the heating pipes beneath the lumber,
it was found that although the air passed upward through
most of the spaces it was actually descending through
others, so that very unequal drying resulted. While
edge piling would at first thought seem ideal for the freest
circulation in an ordinary kiln with steam pipes below, it
in fact produces an indeterminate condition; air columns
may pass downward through some channels as well as upward
through others, and probably stagnate in still others.
Nevertheless, edge piling is greatly superior to flat piling
where the heating system is below the lumber.

From experiments and from study of conditions in
commercial kilns the idea was developed of so arranging
the parts of the kiln and the pile of lumber that advantage
might be taken of this cooling of the air to assist the circulation.
That this can be readily accomplished without
doing away with the present features of regulation of
humidity by means of a spray of water is clear from Fig.
30, which shows a cross-section of the improved humidity-regulated
dry kiln.

In the form shown in the sketch a chamber or flue B
runs through the center near the bottom. This flue is
only about 6 or 7 feet in height and, together with the
water spray F and the baffle plates DD, constitutes the
humidity-control feature of the kiln. This control of
humidity is affected by the temperature of the water
used in the spray. This spray completely saturates the
air in the flue B at whatever predetermined temperature[163]
is required. The baffle plates DD are to separate all
entrained particles of water from the air, so that it is delivered
to the heaters in a saturated condition at the required
temperature. This temperature is, therefore, the
dew point of the air when heated above, and the method
of humidity control may therefore be called the dew-point
method. It is a very simple matter by means of the humidity
diagram (see Fig. 93), or by a hygrodeik (Fig. 94),
to determine what dew-point temperature is needed for
any desired humidity above the heaters.

Besides regulating the humidity the spray F also acts as
an ejector and forces circulation of air through the flue B.
The heating system H is concentrated near the outer
walls, so as to heat the rising column of air. The temperature
within the drying chamber is controlled by means
of any suitable thermostat, actuating a valve on the main
steam line. The lumber is piled in such a way that the
stickers slope downward toward the sides of the kiln.

M is an auxiliary steam spray pointing downward for
use at very high temperatures. C is a gutter to catch
the precipitation and conduct it back to the pump, the
water being recirculated through the sprays. G is a pipe
condenser for use toward the end of the drying operation.
K is a baffle plate for diverting the heated air and at the
same time shielding the under layers of boards from direct
radiation of the steam pipes.

The operation of the kiln is simple. The heated air
rises above the pipes HH and between the piles of lumber.
As it comes in contact with the piles, portions of it are
cooled and pass downward and outward through the layers
of boards into the space between the condensers GG.
Here the column of cooled air descends into the spray flue
B, where its velocity is increased by the force of the water
spray. It then passes out from the baffle plates to the
heaters and repeats the cycle.

One of the greatest advantages of this natural circulation
method is that the colder the lumber when placed in
the kiln the greater is the movement produced, under the
very conditions which call for the greatest circulation—just
the opposite of the direct-circulation method. This[164]
is a feature of the greatest importance in winter, when the
lumber is put into the kiln in a frozen condition. One
truckload of lumber at 60 per cent moisture may easily
contain over 7,000 pounds of ice.

In the matter of circulation the kiln is, in fact, seldom
regulatory—the colder the lumber the greater the circulation
produced, with the effect increased toward the cooler
and wetter portions of the pile.

Preliminary steaming may be used in connection with
this kiln, but experiments indicate that ordinarily it is
not desirable, since the high humidity which can be secured
gives as good results, and being at as low a temperature
as desired, much better results in the case of certain difficult
woods like oak, eucalyptus, etc., are obtained.

This kiln has another advantage in that its operation
is entirely independent of outdoor atmospheric conditions,
except that barometric pressure will effect it slightly.

KILN-DRYING

Remarks

Drying is an essential part of the preparation of wood
for manufacture. For a long time the only drying process
used or known was air-drying, or the exposure of wood to
the gradual drying influences of the open air, and is what
has now been termed “preliminary seasoning.” This
method is without doubt the most successful and effective
seasoning, because nature performs certain functions in
air-drying that cannot be duplicated by artificial means.
Because of this, hardwoods, as a rule, cannot be successfully
kiln-dried green or direct from the saw.

Within recent years, considerable interest is awakening
among wood users in the operation of kiln-drying.
The losses occasioned in air-drying and in improper kiln-drying,
and the necessity for getting material dry as
quickly as possible from the saw, for shipping purposes
and also for manufacturing, are bringing about a realization
of the importance of a technical knowledge of the
subject.[165]

The losses which occur in air-drying wood, through
checking, warping, staining, and rotting, are often greater
than one would suppose. While correct statistics of this
nature are difficult to obtain, some idea may be had of
the amount of degrading of the better class of lumber.
In the case of one species of soft wood, Western larch, it
is commonly admitted that the best grades fall off sixty
to seventy per cent in air-drying, and it is probable that
the same is true in the case of Southern swamp oaks. In
Western yellow pine, the loss is great, and in the Southern
red gum, it is probably as much as thirty per cent. It
may be said that in all species there is some loss in air-drying,
but in some easily dried species such as spruce,
hemlock, maple, etc., it is not so great.

It would hardly be correct to state at the present time
that this loss could be entirely prevented by proper methods
of kiln-drying the green lumber, but it is safe to say that
it can be greatly reduced.

It is well where stock is kiln-dried direct from the saw
or knife, after having first been steamed or boiled—as
in the case of veneers, etc.,—to get them into the kiln
while they are still warm, as they are then in good condition
for kiln-drying, as the fibres of the wood are soft
and the pores well opened, which will allow of forcing
the evaporation of moisture without much damage being
done to the material.

With softwoods it is a common practice to kiln-dry
direct from the saw. This procedure, however, is ill
adapted for the hardwoods, in which it would produce
such warping and checking as would greatly reduce the
value of the product. Therefore, hardwoods, as a rule,
are more or less thoroughly air-dried before being placed
in the dry kiln, where the residue of moisture may be
reduced to within three or four per cent, which is much
lower than is possible by air-drying only.

It is probable that for the sake of economy, air-drying
will be eliminated in the drying processes of the future without
loss to the quality of the product, but as yet no method
has been discovered whereby this may be accomplished.

The dry kiln has been, and probably still is, one of the[166]
most troublesome factors arising from the development
of the timber industry. In the earlier days, before power
machinery for the working-up of timber products came
into general use, dry kilns were unheard-of, air-drying
or seasoning was then relied upon solely to furnish the
craftsman with dry stock from which to manufacture his
product. Even after machinery had made rapid and
startling strides on its way to perfection, the dry kiln remained
practically an unknown quantity, but gradually,
as the industry developed and demand for dry material
increased, the necessity for some more rapid and positive
method of seasoning became apparent, and the subject of
artificial drying began to receive the serious attention of
the more progressive and energetic members of the craft.

Kiln-drying which is an artificial method, originated
in the effort to improve or shorten the process, by subjecting
the wood to a high temperature or to a draught of
heated air in a confined space or kiln. In so doing, time
is saved and a certain degree of control over the drying
operation is secured.

The first efforts in the way of artificial drying were confined
to aiding or hastening nature in the seasoning process
by exposing the material to the direct heat from fires built
in pits, over which the lumber was piled in a way to expose
it to the heat rays of the fires below. This, of course,
was a primitive, hazardous, and very unsatisfactory
method, to say the least, but it marked the first step in
the evolution of the present-day dry kiln, and in that
particular only is it deserving of mention.

Underlying Principles

In addition to marking the first step in artificial drying,
it illustrated also, in the simplest manner possible, the
three underlying principles governing all drying problems:
(1) The application of heat to evaporate or volatilize the
water contained in the material; (2) with sufficient air
in circulation to carry away in suspension the vapor thus
liberated; and (3) with a certain amount of humidity
present to prevent the surface from drying too rapidly
while the heat is allowed to penetrate to the interior. The[167]
last performs two distinct functions: (a) It makes the
wood more permeable to the passage of the moisture
from the interior of the wood to the surface, and (b) it
supplies the latent heat necessary to evaporate the moisture
after it reaches the surface. The air circulation
is important in removing the moisture after it has
been evaporated by the heat, and ventilation also
serves the purpose of bringing the heat in contact with
the wood. If, however, plain, dry heat is applied to the
wood, the surface will become entirely dry before the interior
moisture is even heated, let alone removed. This
condition causes “case-hardening” or “hollow-horning.”
So it is very essential that sufficient humidity be maintained
to prevent the surface from drying too rapidly,
while the heat is allowed to penetrate to the interior.

This humidity or moisture is originated by the evaporation
from the drying wood, or by the admission of steam
into the dry kiln by the use of steam spray pipes, and is
absolutely necessary in the process of hastening the drying
of wood. With green lumber it keeps the sap near
the surface of the piece in a condition that allows the
escape of the moisture from its interior; or, in other words,
it prevents the outside from drying first, which would
close the pores and cause case-hardening.

The great amount of latent heat necessary to evaporate
the water after it has reached the surface is shown by the
fact that the evaporation of only one pound of water will
extract approximately 66 degrees from 1,000 cubic feet
of air, allowing the air to drop in temperature from 154 to
84 degrees Fahrenheit. In addition to this amount of heat,
the wood and the water must also be raised to the temperature
at which the drying is to be accomplished.

It matters not what type of dry kiln is used, source or
application of heating medium, these underlying principles
remain the same, and must be the first things considered
in the design or selection of the equipment necessary for
producing the three essentials of drying: Heat, humidity,
and circulation.

Although these principles constitute the basis of all
drying problems and must, therefore, be continually[168]
carried in mind in the consideration of them, it is equally
necessary to have a comprehensive understanding of the
characteristics of the materials to be dried, and its action
during the drying process. All failures in the past, in
the drying of timber products, can be directly attributed
to either the kiln designer’s neglect of these things, or his
failure to carry them fully in mind in the consideration
of his problems.

Wood has characteristics very much different from those
of other materials, and what little knowledge we have
of it and its properties has been taken from the accumulated
records of experience. The reason for this imperfect
knowledge lies in the fact that wood is not a homogeneous
material like the metals, but a complicated structure, and
so variable that one stick will behave in a manner widely
different from that of another, although it may have been
cut from the same tree.

The great variety of woods often makes the mere distinction
of the kind or species of the tree most difficult.
It is not uncommon to find men of long experience disagree
as to the kind of tree a certain piece of lumber was
cut from, and, in some cases, there is even a wide difference
in the appearance and evidently the structure of
timber cut from the same tree.

Objects of Kiln-drying

The objects of kiln-drying wood may be placed under
three main headings: (1) To reduce shipping expenses;
(2) to reduce the quantity necessary to maintain in stock;
and (3) to reduce losses in air-drying and to properly
prepare the wood for subsequent use. Item number 2
naturally follows as a consequence of either 1 or 3. The
reduction in weight on account of shipping expenses is
of greatest significance with the Northwestern lumbermen
in the case of Douglas fir, redwood, Western red cedar,
sugar pine, bull pine, and other softwoods.

Very rapid methods of rough drying are possible with
some of these species, and are in use. High temperatures
are used, and the water is sometimes boiled off from the
wood by heating above 212 degrees Fahrenheit. These[169]
high-temperature methods will not apply to the majority
of hardwoods, however, nor to many of the softwoods.

It must first of all be recognized that the drying of
lumber is a totally different operation from the drying
of a fabric or of thin material. In the latter, it is largely
a matter of evaporated moisture, but wood is not only
hygroscopic and attracts moisture from the air, but its
physical behavior is very complex and renders the extraction
of moisture a very complicated process.

An idea of its complexity may be had by mentioning some
of the conditions which must be contended with. Shrinkage
is, perhaps, the most important. This is unequal
in different directions, being twice as great tangentially
as radially and fifty times as great radially as longitudinally.
Moreover, shrinkage is often unequal in different
portions of the same piece. The slowness of the transfusion
of moisture through the wood is an important factor. This
varies with different woods and greatly in different directions.
Wood becomes soft and plastic when hot and moist,
and will yield more or less to internal stresses. As some
species are practically impervious to air when wet, this
plasticity of the cell walls causes them to collapse as the
water passes outward from the cell cavities. This difficulty
has given much trouble in the case of Western red
cedar, and also to some extent in redwood. The unequal
shrinkage causes internal stresses in the wood as it dries,
which results in warping, checking, case-hardening, and
honeycombing. Case-hardening is one of the most common
defects in improperly dried lumber. It is clearly
shown by the cupping of the two halves when a case-hardened
board is resawed. Chemical changes also occur
in the wood in drying, especially so at higher temperatures,
rendering it less hygroscopic, but more brittle. If dried
too much or at too high a temperature, the strength and
toughness is seriously reduced.

Conditions of Success

Commercial success in drying therefore requires that
the substance be exposed to the air in the most efficient
manner; that the temperature of the air be as high as the[170]
substance will stand without injury, and that the air change
or movement be as rapid as is consistent with economical
installation and operation. Conditions of success therefore
require the observance of the following points, which
embody the basic principles of the process: (1) The
timber should be heated through before drying begins.
(2) The air should be very humid at the beginning of the
drying process, and be made drier only gradually. (3) The
temperature of the lumber must be maintained uniformly
throughout the entire pile. (4) Control of the drying
process at any given temperature must be secured by
controlling the relative humidity, not by decreasing the
circulation. (5) In general, high temperatures permit
more rapid drying than do lower temperatures. The
higher the temperature of the lumber, the more efficient
is the kiln. It is believed that temperatures as high as
the boiling point are not injurious to most woods, providing
all other fundamentally important features are
taken care of. Some species, however, are not able to
stand as high temperatures as others, and (6) the degree
of dryness attained, where strength is the prime requisite,
should not exceed that at which the wood is to be used.

Different Treatment according to Kind

The rapidity with which water may be evaporated, that
is, the rate of drying, depends on the size and shape of
the piece and on the structure of the wood. Thin stock
can be dried much faster than thick, under the same conditions
of temperature, circulation, and humidity. Pine
can be dried, as a general thing, in about one third of the
time that would be required for oak of the same thickness,
although the former contains the more water of the two.
Quarter-sawn oak usually requires half again as long as
plain oak. Mahogany requires about the same time as
plain oak; ash dries in a little less time, and maple, according
to the purpose for which it is intended, may be dried
in one fifth the time needed for oak, or may require a
slightly longer treatment. For birch, the time required
is from one half to two thirds, and for poplar and basswood,
from, one fifth to one third that required for oak.[171]