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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.
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.
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.
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
| Sycamore | Beech | Birch |
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.
Pores all minute or indistinct, evenly distributed throughout annual ring.
( a ) With conspicuously broad rays.
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.
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.
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.
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.
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.
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.
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.
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.