wood (redirected from Woodless)

wood, botanically, the xylem tissue that forms the bulk of the stem of a woody plant. Xylem conducts sap upward from the roots to the leaves, stores food in the form of complex carbohydrates, and provides support; it is made up of various types of cells specialized for each of these purposes. Among them are tracheids, elongated conduction and support cells; parenchyma (food storage) cells, some of which form rays for transverse conduction; xylem vessels, formed of hollow cells joined end to end; and fiber cells that reinforce these tubes. In the conifers the xylem is made up mainly of tracheids, thus presenting a uniform, nonporous appearance; their wood is called softwood. Deciduous trees have more complex xylem, permeated by vessels, and are called hardwoods, although the description is sometimes inaccurate.

The xylem is formed in the growing season by the cambium; in temperate regions the cells formed in the spring are larger in diameter than those formed in the summer, and this results in the annual rings observable in cross section. The new cells lose their protoplasm as they form the various tissues; the older, nonfunctional cells become plugged up, darken in color, and often accumulate bitter or poisonous substances (tannins, dyes, resins, and gums). This inner wood (the heartwood, as opposed to the functional sapwood) is valued for outdoor construction because of its resistance to moisture and to decay-producing organisms.

Commercial Uses

Freshly cut wood contains much moisture and tends to warp and split as it dries. Lumber is therefore seasoned before use—dried either slowly in the sun and air or more quickly by artificial means (kiln drying). Seasoning increases wood's buoyancy, strength, elasticity, and durability. Although synthetic materials have supplanted wood in many of its former uses, it is still widely employed for furniture, floors, railway ties, paper manufacture, and innumerable other purposes. Wood distillation yields methyl alcohol, wood tar, acetic acid, acetone, and turpentine; charcoal is made by burning or heating wood in insufficient air to consume it.

The wood of different species of trees varies considerably in weight, strength, and appearance. Softwood is normally uniform in grain (texture) and color; hardwood, in which the rays are more prominent and the arrangement of tissues is variable, produces lumber in which the grain may run vertically or horizontally and be coarse or smooth. The manner in which a log is cut results in lumber with thin or wide ray markings. A log cut horizontally shows the concentric annual rings; lengthwise cuts through the center are marked by thin vertical ray lines; and lengthwise cuts through the outer sections show the wood's characteristic wavy grain and wider ray markings, prized for their beauty. The rarer decorative woods may be cut in thin layers and glued to other wood structures (see veneer). Plywood, made of thin layers of wood glued so that the grains alternate in direction, makes an especially strong construction material. For some applications composition board offers another inexpensive substitute. Pressure-treated wood is lumber that has had a preservative forced into it under pressure.

Bibliography

See H. Cone, Wood Structure and Identification (1979); H. Bucksh, Dictionary of Wood and Woodworking Practice (2 vol., 1986).

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wood

Cross section of a tree trunk. Wood is secondary xylem produced by growth of the vascular cambium …

(credit: © Merriam-Webster Inc.)

Hard, fibrous material formed by the accumulation of secondary xylem produced by the vascular cambium. It is the principal strengthening tissue found in the stems and roots of trees and shrubs. Wood forms around a central core (pith) in a series of concentric layers called growth rings. A cross section of wood shows the distinction between heartwood and sapwood. Heartwood, the central portion, is darker and composed of xylem cells that are no longer active in the life processes of the tree. Sapwood, the lighter area surrounding the heartwood, contains actively conducting xylem cells. Wood is one of the most abundant and versatile natural materials on earth, and unlike coal, ores, and petroleum, is renewable with proper care. The most widely used woods come from two groups of trees: the conifers, or softwoods (e.g., pine, spruce, fir), and the broadleaves, or hardwoods (e.g., oak, walnut, maple). Trees classified as hardwoods are not necessarily harder than softwoods (e.g., balsa, a hardwood, is one of the softest woods). Density and moisture content affect the strength of wood; in addition to load-bearing strength, other variable factors often tested include elasticity and toughness. Wood is insulating to heat and electricity and has desirable acoustical properties. Some identifying physical characteristics of wood include colour, odour, texture, and grain (the direction of the wood fibres). Some 10,000 different wood products are commercially available, ranging from lumber and plywood to paper, from fine furniture to toothpicks. Chemically derived products from wood and wood residues include cellophane, charcoal, dyestuffs, explosives, lacquers, and turpentine. Wood is also used for fuel in many parts of the world.

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wood

knocking on it averts dire consequences. [Western Culture: Misc.]

See : Protection