OUR COMMON WOODS: THEIR IDENTIFICATION, PROPERTIES AND USES
Woods have different values for various practical purposes because of
their peculiarities in structure. A knowledge of the structural parts of
wood is therefore necessary as a means of recognizing the wood and of
determining why one piece is stronger, heavier, tougher, or better
adapted for a given service than another.
Structure of wood: If one examines a cross-section of the bole of a
tree, he will note that it is composed of several distinct parts, as
shown in Fig. 145. At the very center is a small core of soft tissue
known as the _pith_. It is of much the same structure as the pith of
cornstalk or elder, with which all are familiar. At the outside is
the _bark_, which forms a protective covering over the entire woody
system. In any but the younger stems, the bark is composed of an
inner, live layer, and an outer or dead portion.
Between the pith at the center and the bark at the outside is the
wood. It will be noted that the portion next to the bark is white or
yellowish in color. This is the _sapwood_. It is principally through
the sapwood that the water taken in by the roots is carried up to
the leaves. In some cases the sapwood is very thin and in others it
is very thick, depending partly on the kind of tree, and partly on
its age and vigor. The more leaves on a tree the more sapwood it
must have to supply them with moisture.
[Illustration: FIG. 144.--Pine Wood. (Magnified 30 times.)]
Very young trees are all sapwood, but, as they get older, part of
the wood is no longer needed to carry sap and it becomes
_heartwood_. Heartwood is darker than the sapwood, sometimes only
slightly, but in other instances it may vary from a light-brown
color to jet black. It tends to fill with gums, resins, pigments and
other substances, but otherwise its structure is the same as that of
the sapwood.
[Illustration: FIG. 145.--Cross-section of Oak.]
The wood of all our common trees is produced by a thin layer of
cells just beneath the bark, the _cambium_. The cambium adds new
wood on the outside of that previously formed and new bark on the
inside of the old bark. A tree grows most rapidly in the spring, and
the wood formed at that time is much lighter, softer and more
porous than that formed later in the season, which is usually quite
hard and dense. These two portions, known as _early wood_ or spring
wood, and _late wood_ or summer wood, together make up one year's
growth and are for that reason called _annual rings_. Trees such as
palms and yucca do not grow in this way, but their wood is not
important enough in this country to warrant a description.
[Illustration: FIG. 146.--White Oak Wood. (Magnified 20 times.)]
If the end of a piece of oak wood is examined, a number of lines
will be seen radiating out toward the bark like the spokes in a
wheel. These are the _medullary rays_. They are present in all
woods, but only in a few species are they very prominent to the
unaided eye. These rays produce the "flakes" or "mirrors" that make
quartersawed (radially cut) wood so beautiful. They are thin plates
or sheets of cells lying in between the other wood cells. They
extend out into the inner bark.
While much may be seen with the unaided eye, better results can be
secured by the use of a good magnifying glass. The end of the wood
should be smoothed off with a very sharp knife; a dull one will
tear and break the cells so that the structure becomes obscured.
With any good hand lens a great many details will then appear which
before were not visible. In the case of some woods like oak, ash,
and chestnut, it will be found that the early wood contains many
comparatively large openings, called _pores_, as shown in Figs. 146
and 147. Pores are cross-sections of vessels which are little
tube-like elements running throughout the tree. The vessels are
water carriers. A wood with its large pores collected into one row
or in a single band is said to be _ring-porous_. Fig. 146 shows such
an arrangement. A wood with its pores scattered throughout the
year's growth instead of collected in a ring is _diffuse-porous_.
Maple, as shown in Fig. 152, is of this character.
[Illustration: FIG. 147.--Example of the Black Oak Group. (Quercus
coccinea.) (Magnified 20 times.)]
All of our broadleaf woods are either ring-porous or diffuse-porous,
though some of them, like the walnut, are nearly half way between
the two groups.
If the wood of hickory, for example, be examined with the magnifying
lens, it will be seen that there are numerous small pores in the
late wood, while running parallel with the annual rings are little
white lines such as are shown in Fig. 149. These are lines of _wood
parenchyma_. Wood parenchyma is found in all woods, arranged
sometimes in tangential lines, sometimes surrounding the pores and
sometimes distributed over the cross-section. The dark, horn-like
portions of hickory and oak are the _woodfibers_. They give the
strength to wood.
In many of the diffuse-porous woods, the pores are too small to be
seen with the unaided eye, and in some cases they are not very
distinct even when viewed with a magnifier. It is necessary to study
such examples closely in order not to confuse them with the woods of
conifers.
The woods of conifers are quite different in structure from
broadleaf woods, though the difference may not always stand out
prominently. Coniferous woods have no pores, their rays are always
narrow and inconspicuous, and wood parenchyma is never prominent.
The woods of the pines, spruces, larches, and Douglas fir differ
from those of the other conifers in having _resin ducts_, Fig. 144.
In pines these are readily visible to the naked eye, appearing as
resinous dots on cross-sections and as pin scratches or dark lines
on longitudinal surfaces. The presence or absence of resin ducts is
a very important feature in identifying woods, hence it is very
important to make a careful search for them when they are not
readily visible.
How to identify a specimen of wood: The first thing to do in identifying
a piece of wood is to cut a smooth section at the end and note
(without the magnifier) the color, the prominence of the rays and
pores, and any other striking features. If the pores are readily
visible, the wood is from a broadleaf tree; if the large pores are
collected in a ring it belongs to the ring-porous division of the
broadleaf woods. If the rays are quite conspicuous and the wood is
hard and heavy, it is oak, as the key given later will show. Close
attention to the details of the key will enable one to decide to
what group of oaks it belongs.
In most cases the structure will not stand out so prominently as in
oak, so that it is necessary to make a careful study with the hand
lens. If pores appear, their arrangement, both in the early wood and
in the late wood, should be carefully noted; also whether the pores
are open or filled with a froth-like substance known as _tyloses_.
Wood parenchyma lines should be looked for, and if present, the
arrangement of the lines should be noted.
[Illustration: FIG. 148.--(Magnified about 8 times.)]
If no pores appear under the magnifying lens, look closely for resin
ducts. If these are found, note whether they are large or small,
numerous or scattered, open or closed, lighter or darker than the
wood. Note also whether the late wood is very heavy and hard,
showing a decided contrast to the early wood, or fairly soft and
grading into the early wood without abrupt change. Weigh the piece
in your hand, smell a fresh-cut surface to detect the odor, if any,
and taste a chip to see if anything characteristic is discoverable.
Then turn to the following key:
KEY
I. WOODS WITHOUT PORES--CONIFERS OR SO-CALLED "SOFTWOODS"
A. Woods with resin ducts.
1. Pines. Fig. 144. Resin ducts numerous, prominent, fairly evenly
distributed. Wood often pitchy. Resinous odor distinct. Clear
demarcation between heart and sapwood. There are two groups of
pines--soft and hard.
(a) Soft Pines. Wood light, soft, not strong, even-textured, very
easy to work. Change from early wood to late wood is gradual and the
difference in density is not great.
(b) Hard Pines. Wood variable but typically rather heavy, hard and
strong, uneven textured, fairly easy to work. Change from early wood
to late wood is abrupt and the difference in density and color is
very marked, consequently alternate layers of light and dark wood
show. The wood of nearly all pines is very extensively employed in
construction work and in general carpentry.
2. Douglas fir. Resin ducts less numerous and conspicuous than in the
pines, irregularly distributed, often in small groups. Odorless or
nearly so. Heartwood and sapwood distinct. The wood is of two kinds.
In one the growth rings are narrow and the wood is rather light and
soft, easy to work, reddish yellow in color; in the other the growth
rings are wide, the wood is rather hard to work, as there is great
contrast between the weak early wood and the very dense late wood of
the annual rings.
Douglas fir is a tree of great economic importance on the Pacific
Coast. The wood is much like hard pine both in its appearance and
its uses.
3. Spruces. Resin ducts few, small, unevenly distributed; appearing
mostly as white dots. Wood not resinous; odorless. The wood is white
or very light colored with a silky luster and with little contrast
between heart and sapwood. It is a great deal like soft pine, though
lighter in color and with much fewer and smaller resin ducts. The
wood is used for construction, carpentry, oars, sounding boards for
musical instruments, and paper pulp.
4. Tamarack. Resin ducts the same as in the spruces. The color of the
heartwood is yellowish or russet brown; that of the distinct sapwood
much lighter. The wood is considerably like hard pine, but lacks the
resinous odor and the resin ducts are much fewer and smaller.
The wood is used largely for cross-ties, fence posts, telegraph and
telephone poles, and to a limited extent for lumber in general
construction.
B. Woods without resin ducts.
1. Hemlock. The wood has a disagreeable, rancid odor, is splintery, not
resinous, with decided contrast between early and late wood. Color
light brown with a slight tinge of red, the heart little if any
darker than the sapwood. Hemlock makes a rather poor lumber which is
used for general construction, also for cross-ties, and pulp.
2. Balsam fir. Usually odorless, not splintery, not resinous, with
little contrast between early and late wood. Color white or very
light brown with a pinkish hue to the late wood. Heartwood little if
any darker than the sapwood. Closely resembles spruce, from which it
can be distinguished by its absence of resin ducts.
The wood is used for paper pulp in mixture with spruce. Also for
general construction to some extent.
3. Cypress. Odorless except in dark-colored specimens which are somewhat
rancid. Smooth surface of sound wood looks and feels greasy or waxy.
Moderate contrast between early and late wood. Color varies from
straw color to dark brown, often with reddish and greenish tinge.
Heartwood more deeply colored than the sapwood but without distinct
boundary line.
Wood used in general construction, especially in places where
durability is required; also for shingles, cooperage, posts, and
poles.
4. Red Cedar. Has a distinct aromatic odor. Wood uniform-textured; late
wood usually very thin, inconspicuous. Color deep reddish brown or
purple, becoming dull upon exposure; numerous minute red dots often
visible under lens. Sapwood white. Red cedar can be distinguished
from all the other conifers mentioned by the deep color of the wood
and the very distinct aromatic odor.
Wood largely used for pencils; also for chests and cabinets, posts,
and poles. It is very durable in contact with the ground.
_Western red cedar_ is lighter, softer, less deeply colored and less
fragrant than the common Eastern cedar. It grows along the Pacific
Coast and is extensively used for shingles throughout the country.
5. Redwood. Wood odorless and tasteless, uniform-textured, light and
weak, rather coarse and harsh. Color light cherry. Close inspection
under lens of a small split surface will reveal many little resin
masses that appear as rows of black or amber beads which are
characteristic of this wood.
Redwood is confined to portions of the Pacific Coast. It is used for
house construction, interior finish, tanks and flumes, shingles,
posts, and boxes. It is very durable.
II. WOODS WITH PORES--BROADLEAF, OR SO-CALLED "HARDWOODS"
A. Ring-porous.
1. Woods with a portion of the rays very large and conspicuous.
Oak. The wood of all of the oaks is heavy, hard, and strong. They may be
separated into two groups. The white oaks and the red or black oaks.
(a) White oaks. Pores in early wood plugged with tyloses, collected in
a few rows. Fig. 146. The transition from the large pores to the
small ones in the late wood is abrupt. The latter are very small,
numerous, and appear as irregular grayish bands widening toward the
outer edge of the annual ring. Impossible usually to see into the
small pores with magnifier.
(b) Red or black oaks. Pores are usually open though tyloses may
occur, Fig. 147; the early wood pores are in several rows and the
transition to the small ones in late wood is gradual. The latter are
fewer, larger and more distinct than in white oak and it is
possible to see into them with a hand lens.
The wood of the oaks is used for all kinds of furniture, interior
finish, cooperage, vehicles, cross-ties, posts, fuel, and
construction timber.
2. Woods with none of the rays large and conspicuous.
(a) Pores in late wood small and in radial lines, wood parenchyma in
inconspicuous tangential lines.
Chestnut. Pores in early wood in a broad band, oval in shape, mostly
free from tyloses. Pores in late wood in flame-like radial white
patches that are plainly visible without lens. Color medium brown.
Nearly odorless and tasteless. Chestnut is readily separated from
oak by its weight and absence of large rays; from black ash by the
arrangement of the pores in the late wood; from sassafras by the
arrangement of the pores in the late wood, the less conspicuous
rays, and the lack of distinct color.
The wood is used for cross-ties, telegraph and telephone poles,
posts, furniture, cooperage, and tannin extract. Durable in contact
with the ground.
(b) Pores in late wood small, not radially arranged, being distributed
singly or in groups. Wood parenchyma around pores or extending wing-like
from pores in late wood, often forming irregular tangential lines.
1. Ash. Pores in early wood in a rather broad band (occasionally
narrow), oval in shape, see Fig. 148, tyloses present. Color brown
to white, sometimes with reddish tinge to late wood. Odorless and
tasteless. There are several species of ash that are classed as
white ash and one that is called black or brown ash.
(a) White ash. Wood heavy, hard, strong, mostly light colored except
in old heartwood, which is reddish. Pores in late wood, especially
in the outer part of the annual ring, are joined by lines of wood
parenchyma.
(b) Black ash. Wood more porous, lighter, softer, weaker, and darker
colored than white ash. Pores in late wood fewer and larger and
rarely joined by tangential lines of wood parenchyma.
The wood of the ashes is used for wagon and carriage stock,
agricultural implements, oars, furniture, interior finish, and
cooperage. It is the best wood for bent work.
[Illustration: FIG. 149.--Hickory Wood. (Magnified 45 times.)]
2. Locust. Pores in early wood in a rather narrow band, round, variable
in size, densely filled with tyloses. Color varying from golden
yellow to brown, often with greenish hue. Very thin sapwood, white.
Odorless and almost tasteless. Wood extremely heavy and hard,
cutting like horn. Locust bears little resemblance to ash, being
harder, heavier, of a different color, with more distinct rays, and
with the pores in late wood in larger groups.
The wood is used for posts, cross-ties, wagon hubs, and insulator
pins. It is very durable in contact with the ground.
(c) Pores in late wood comparatively large, not in groups or lines.
Wood parenchyma in numerous fine but distinct tangential lines.
[Illustration: FIG. 150.--Elm. (Magnified 25 times.)]
Hickory, Fig. 149. Pores in early wood moderately large, not abundant,
nearly round, filled with tyloses. Color brown to reddish brown;
thick sapwood, white. Odorless and tasteless. Wood very heavy, hard,
and strong. Hickory is readily separated from ash by the fine
tangential lines of wood parenchyma and from oak by the absence of
large rays.
The wood is largely used for vehicles, tool handles, agricultural
implements, athletic goods, and fuel.
(d) Pores in late wood small and in conspicuous wavy tangential bands.
Wood parenchyma not in tangential lines.
Elm. Pores in early wood not large and mostly in a single row, Fig. 150
(several rows in slippery elm), round, tyloses present. Color brown,
often with reddish tinge. Odorless and tasteless. Wood rather heavy
and hard, tough, often difficult to split. The peculiar arrangement
of the pores in the late wood readily distinguishes elm from all
other woods except _hackberry_, from which it may be told by the
fact that in elm the medullary rays are indistinct, while they are
quite distinct in hackberry; moreover, the color of hackberry is
yellow or grayish yellow instead of brown or reddish brown as in
elm.
The wood is used principally for slack cooperage; also for hubs,
baskets, agricultural implements, and fuel.
[Illustration: FIG. 151.--(Magnified about 8 times.)]
B. Diffuse-porous.
1. Pores varying in size from rather large to minute, the largest being
in the early wood. Intermediate between ring-porous and diffuse-porous.
Black Walnut. Color rich dark or chocolate brown. Odor mild but
characteristic. Tasteless or nearly so. Wood parenchyma in numerous,
fine tangential lines. Wood heavy and hard, moderately stiff and
strong. The wood is used principally for furniture, cabinets,
interior finish, moulding, and gun stocks.
2. Pores all minute or indistinct, evenly distributed throughout annual
ring.
(a) With conspicuously broad rays.
1. Sycamore. Fig. 151. Rays practically all broad. Color light brown,
often with dark stripes or "feather grain." Wood of medium weight
and strength, usually cross-grained, difficult to split.
The wood is used for general construction, woodenware, novelties,
interior finish, and boxes.
2. Beech. With only a part of the rays broad, the others very fine, Fig.
151. Color pale reddish brown to white; uniform. Wood heavy, hard,
strong, usually straight-grained.
The wood is used for cheap furniture, turnery, cooperage,
woodenware, novelties, cross-ties, and fuel. Much of it is
distilled.
(b) Without conspicuously broad rays.
1. Cherry. Rays rather fine but very distinct. Color of wood reddish
brown. Wood rather heavy, hard, and strong.
The wood is used for furniture, cabinet work, moulding, interior
finish, and miscellaneous articles.
2. Maple, Fig. 152. With part of the rays rather broad and conspicuous,
the others very fine. Color light brown tinged with red. The wood of
the hard maple is very heavy, hard and strong; that of the soft
maples is rather light, fairly strong. Maple most closely resembles
birch, but can be distinguished from it through the fact that in
maple the rays are considerably more conspicuous than in birch.
The wood is used for slack cooperage, flooring, interior finish,
furniture, musical instruments, handles, and destructive
distillation.
3. Tulip-tree, yellow poplar or whitewood. Rays all fine but distinct.
Color yellow or brownish yellow; sapwood white. Wood light and soft,
straight-grained, easy to work.
The wood is used for boxes, woodenware, tops and bodies of vehicles,
interior finish, furniture, and pulp.
4. Red or sweet gum. Rays all fine but somewhat less distinct than in
tulip tree. Color reddish brown, often with irregular dark streaks
producing a "watered" effect on smooth boards; thick sapwood,
grayish white. Wood rather heavy, moderately hard, cross-grained,
difficult to work.
The best grades of figured red gum resemble Circassian walnut, but
the latter has much larger pores unevenly distributed and is less
cross-grained than red gum.
The wood is used for finishing, flooring, furniture, veneers, slack
cooperage, boxes, and gun stocks.
[Illustration: FIG. 152.--Maple. (Magnified 25 times.)]
5. Black or sweet birch, Fig. 151. Rays variable in size but all rather
indistinct. Color brown, tinged with red, often deep and handsome.
Wood heavy, hard, and strong, straight-grained, readily worked. Is
darker in color and has less prominent rays than maple.
The wood is used for furniture, cabinet work, finishing, and
distillation.
6. Cottonwood. Rays extremely fine and scarcely visible even under lens.
Color pale dull brown or grayish brown. Wood light, soft, not
strong, straight-grained, fairly easy to work. Cottonwood can be
separated from other light and soft woods by the fineness of its
rays, which is equaled only by willow, which it rather closely
resembles. The wood is largely used for boxes, general construction,
lumber, and pulp.
How to judge the quality of wood: To know the name of a piece of wood
means, in a general way, to know certain qualities that are common
to all other pieces of wood of that species, but it does not explain
the special peculiarities of the piece in question or why that
particular piece is more suitable or unsuitable for a particular
purpose than another piece of the same species. The mere
identification of the wood does not explain why a particular piece
is tougher, stronger or of darker color than another piece of the
same species or even of the same tree. The reason for these special
differences lies in the fact that wood is not a homogeneous material
like metal. Within the same tree different parts vary in quality.
The heartwood is generally heavier and of deeper color than the
sapwood. The butt is superior to the top wood, and the manner in
which the wood was sawed and dried will affect its quality. Knots,
splits, checks, and discoloration due to incipient decay are defects
worth considering. Wood that looks lusterless is usually defective,
because the lack of luster is generally due to disease. Woods that
are hard wear best. Hardness can be determined readily by striking
the wood with a hammer and noting the sound produced. A clear,
ringing sound is a sign of hardness. The strength of a piece of wood
can be judged by its weight after it is well dried. Heavy woods are
usually strong. A large amount of late wood is an indication of
strength and the production of a clear sound when struck with a
hammer is also an evidence of strength.