Wood (A. S. Wudu), the substance forming the body of the trunk and branches of a tree. The stems Of flowering plants are made up of cells of two kinds; the soft parts consist of thin and but little elongated cells, which together form cellular tissue, and running through these are elongated tough and fibre-like cells forming woody tissue. In stems of only one season's duration, the proportion of woody tissue is small, and these are called herbaceous, and the plants herbs. In stems which last from year to year the woody tissue largely preponderates over the cellular, and such stems furnish the substance known as wood. The characters of cellular and woody tissue are given under Plant, and in that article will also be found an account of the manner of the growth and annual increase of stems, and matters relating to their structure which have a direct relation to their value and utility as wood. The stems of endogens, while they are often of great utility in the countries producing them (see Palm), form no appreciable portion of the wood of commerce, and are but little used in temperate climates. Small quantities of Palmyra, porcupine, and speckled woods, from the stems of the cocoanut and other palms, are employed by the makers of ornamental cabinet work, usually in the form of veneers.

The great class of exogenous plants furnishes most of the material known as wood; in these the woody tissue is arranged in a circle around a central pith, and the stem increases in diameter by the formation of an annual layer upon the outside of the old wood; the character of these annual layers, and the manner in which the woody tissue is interpenetrated by plates of cellular tissue, the medullary rays, greatly affect the physical properties of the wood. In chemical composition the different kinds of wood vary greatly; the basis of the wood cells is the same as that of those forming cellular tissue, the principle cellulose (C12H20O10), identical in composition with starch, dextrine, and other principles, and but little different from the sugars. But the cells soon become thickened by the deposit upon their interior of a substance which renders them harder and thicker; this incrusting material was formerly regarded as a distinct principle, to which the name lignine was given, but it is now regarded as a mixture of different substances, which on account of the difficulty of separating them from one another, and from cellulose, have not been analyzed; these, according to their solubility in or relations to chemical reagents, have received the names lignose, lignone, lignine, and lignireose.

Besides these, under the collective name of lignine, various resins, coloring matters, and principles peculiar to particular genera and families of plants, are deposited in the cells, as well as the earthy matters that appear in the ash when wood is burned; some of these deposits constitute the chief value of particular kinds of wood, such as those used in dyeing, or to afford medicinal extracts. In many stems the change produced by the filling up of the cells is very marked, the older wood being much darker and harder; this is called heart wood, and the newer tissues, in which the change has not taken place, are called sap wood. In some cases the heart wood does not become colored, and its cells are but little thickened, as in the white pine, poplar, and tulip tree, technically known as white timber or white woods. The heart wood has ceased to take any part in the vegetative processes, being practically dead, and is of no use to the tree except by mechanically strengthening the trunk; hence it is not rare to find trees in good health from which the centre has been removed by decay. - Trees are usually felled in winter, when vegetation is at rest, though it has been asserted that if they are felled when in full growth, and the bark removed, the drying is more thorough.

The wood, at whatever time the tree may be cut, contains a large amount of moisture, which must be removed to fit it for most uses; when the moisture is allowed to pass off spontaneously, the operation is called seasoning. Logs and beams, whether hewn or sawed, are called timber. The term lumber is applied, chieiiy in the United States, to beams, or to the material sawed into planks and boards, or made into siding, shingles, laths, etc. The sawing is usually done soon after felling, as the operation of seasoning is thereby much hastened; while a solid stick requires several years to dry, boards will be sufficiently seasoned in a single year; seasoning goes on most rapidly under cover, and boards are piled up with sticks between them to allow of a free circulation of air. A previous immersion in water for several months, by removing some soluble substances from the wood, causes it to dry more rapidly afterward. The loss of moisture is accompanied in most cases by shrinkage, the amount of which varies with the kind of wood; in the redwood of California it is imperceptible, and with this no regard is paid to seasoning, while some oaks shrink as much as half an inch to the foot.

For nice work, ordinary seasoning is supplemented by kiln drying, the lumber being exposed in a chamber to currents of air heated to from 100° to 300° F. A patent has been taken for drying lumber on a large scale by means of superheated steam. - The durability of wood, i. e., its power of resisting decay, does not appear to be associated with any other quality, as the most durable woods are found among light and heavy kinds; woods which decay rapidly when exposed to alternate moisture and dryness are often remarkably durable when kept either altogether dry or constantly under water. Larch, a comparatively light wood, and locust, a very heavy one, are almost indestructible under the most unfavorable conditions. Sap wood is generally much less durable than heart wood, even when protected from the weather. (See Dry Rot, and Preservation of Wood.) The properties of density or hardness and specific gravity bear a direct relation to one another. One of the lightest known woods is that of anona palustris of Brazil, which has a specific gravity of 0.206, somewhat lighter than cork; and perhaps the heaviest is the ironbark of Australia (eucalyptus resinifera), of which the specific gravity is 1*426. In the hard and heavy woods, the fibres are very small, the rings of annual growth exceedingly narrow, and the tissues filled with incrusting substances.

Flexibility and elasticity are usually associated qualities, and are found in their greatest perfection in straight-grained woods that are free from knots; as in such woods the fibres are not inclined to interlace, they split readily; the ash, used for oars, lancewood, valued for fishing rods, and hickory, so flexible that when split it is woven into baskets, are woods of this kind. Woods not naturally flexible are made so temporarily by steaming them, and are then bent to the desired shape by powerful machines. The most rigid and toughest woods are those in which the fibres interlace and cross one another at an oblique angle; such woods are difficult to split, and when the parts are torn asunder the surfaces are ragged, in consequence of the breaking of the fibres; among native woods the elm has the quality of toughness in a useful degree, and the hop hornbeam and tupelo are still more difficult to split; lignum vitae is remarkably tough, and, cannot be worked by splitting. - The beauty of woods depends to a great extent upon other qualities than color, though that is important.

Though an exogenous stem is practically made up of rings of growth one with another, many causes interfere with the regularity of this arrangement, and a longitudinal section, instead of showing a series of straight lines, presents a great diversity of figure and variety of light and shade. Much of the beauty of a wood will depend upon the manner of dividing it; if the sawing is done somewhat obliquely, beauties are developed that are not visible when an exact longitudinal cut is made. Much of the beauty of some woods depends upon the medullary rays, already mentioned as plates of cellular tissue running radially across the woody fibres; if the wood, be cut tangentially, only the ends of these rays will be exposed, but by cutting in the direction in which they run, a beautifully varied surface is presented, on which the medullary rays reflect the light in a most pleasing manner. Knots, so often a blemish in lumber for carpentry, are in some woods the cause of great beauty; these knots may be due to that portion of a living branch which is imbedded within the trunk, or to one that in the early life of the tree has perished, and a portion of which remains within the trunk, covered by a more recent growth of wood; either case produces contorted fibres, changes in density, and difference in color, which greatly increase the beauty of the wood.

The portion of a trunk where large branches fork, the burs or gnarls produced by some trees, and the base of the trunk where it is joined by the large roots, all present irregularities of fibre, and are turned to account by the workers of ornamental wood. In sugar maple individual trees are occasionally found in which there is a curious contortion of fibre, producing upon the polished surface the appearance of little projections rising from within small cavities; this is known as birdseye maple. - Colors in woods vary from the almost pure white of the holly to the jet black of ebony; they are sometimes of uniform tint, but frequently, as in mahogany and black walnut, there are different shades of the same color; in rosewood, zebra wood, Amboyna wood, and others, two or more colors are contrasted or blended. But few colored woods fade upon exposure to the light, and in most the color is deepened by time, as in mahogany and black walnut; sometimes the effect of age is produced by applying lime water to the wood before varnishing or oiling it. Staining is often resorted to, and expensive colored woods are imitated in a manner to deceive all but experts. The number of woods esteemed for their odor is few, sandal wood and camphor wood being the principal.

The ornamental woods, or fancy woods as they are termed in trade, are often very costly, and are used in the form of thin slices or veneer, glued to a base of common wood. (See Veneer.) A few years ago a company undertook the manufacture of wood hangings, to be used as a substitute for paper hangings; the wood was sliced off in a continuous roll, as thin as ordinary wall paper, having been first impregnated with glycerine to prevent it from becoming brittle. - One of the principal uses to which wood of nearly all kinds has hitherto been applied by all nations, and still is in many countries, is that of fuel. (See Fuel.) Different kinds of wood vary greatly in their value as fuel. In America the most valuable fire wood for warming apartments, and that used as a standard for comparison, is shell-bark hickory. Sugar maple and beech, named in the order of their value, though very nearly equal, are also very valuable woods for fuel, forming bright solid coals. Among the special uses for which particular woods are peculiarly adapted, there is none more striking than that of boxwood for engravings, for which no substitute approaching it in all requisites has been found; in the qualities of hardness and evenness of texture, allowing of the cutting of lines so delicate that they can only be seen by a strong magnifier, it has no equal.

Elm is preferred to all other woods for wagon hubs. The locust, while it makes the most durable of gate and fence posts, is the most valued wood for making the treenails used in ship building; it is not only used largely in this country, but large quantities are annually exported for the purpose. For oars ash is used almost exclusively; and for gun stocks, walnut. In the articles upon the different trees in this Cyclopedia the special uses to which their wood is adapted are mentioned; and the following list presents the woods in most common use for the purposes named:

Building

Ship building': cedar, pine (deals), fir. larch, elm, oak, locust, teak. Wet constructions (as piles, foundations, flumes, etc.): elm, alder, beech, oak, plane tree, white cedar, and palmetto for wharves. House carpentry: pine, oak, whitewood, chestnut, ash, spruce, sycamore.

Machinery And Millwork

Frames: ash, beech, birch, pine, elm, mahogany, oak. Hollers, etc.: box, lignum vitae, mahogany, service tree. Teeth of wheels: crab tree, hornbeam, locust, service tree. Foundery patterns: alder, pine, mahogany.

Furniture

Common: beech, birch, cedar, cherry, pine, whitewood. Best furniture: Amboyna, black ebony, cherry, mahogany, maple, oak, rosewood, satin wood, sandal wood, chestnut, cedar, tulip wood, walnut, zebra wood, ebony.

The better known woods are classified according to the properties for which they are most valued as follows:

Elasticity

Ash. hazel, hickory, lancewood, chestnut (small), snake wood, yew.

Elasticity And Toughness

Beech, elm, lignum vitae, oak, walnut, hornbeam.

Even Grain (For Carving Or Engraving)

Pear, pine, box, lime tree.

Durability

In dry works: cedar, oak, poplar, yellow pine, chestnut. Exposed to weather: larch, locust.

Coloring Matters

Red: Brazil, braziletto, camwood, logwood, Nicaragua, red sanders, sapan wo«d. Green: green ebony. Yellow: fustic, Zante.

Scent

Camphor wood, cedar, rosewood, sandal wood, satin wood, sassafras.

For the resistance to strain of different woods, see Strength of Materials. - See "Timber and Timber Trees," by Thomas Laslett, timber inspector to the admiralty of Great Britain (London, 1875).