WOOD AND WOODY FIBER. The hard and compact or tough and fibrous parts of plants are composed chiefly of a peculiar kind of vascular tissue (q. v.), which, when compact is wood. It exists chiefly in the stems, frequently in the roots, and also in the inner bark of exogenous plants, which yields many of the most valuable fibers used in the arts, and in the midrib and veins of leaves, same very useful fibers being obtained from the leaves of endogeus. See FIBER. Annual plants contain little or no woody fiber, being composed chiefly of cellular tissue (q.v.), which also forms great part of many herbaceous perennials and of all plants in a very young state. Woody fiber con tists of elongated cells tapering to both extremities, lying close together, and overlapping one another, sometimes much elongated into tubes. Wood is entirely made up of cells of this kind, permeated in exogenous plants by medullary rays. The cells of woody fibre have their walls thickened by successive layers of cellulose and lignine, deposited in their interior, so that they acquire strength. In the inner bark of exogens, woody fiber is mixed with laticiferous vessels (see LATEX) and cellular tissue.
Woody fiber has generally no definite markings on the walls of ,its cells; but these sometimes appear as simple disks, or as disks with smaller circles in the center. These disks are formed by concavities on the outside of the walls of contiguous cells, closely applied to each other, so as to form lenticular cavities between them, as Mr. t proved iu fossil pine-wood, in which he separated lenticular masses of solid matter from between the disks. When the smaller circle appears in the center of the disks, the woody tissue is described as punctated. This is especially the case in coniferce, but it is not absolutely distinctive of them, the same character appearing also in some other plants, as iu Winter's bark. The small circle in the center of the disk is formed by the mouth of a canal, often funnel-shaped. These canals or pores, connecting one cell with another,
are supposed to give to the wood of the coniferce its peculiar fitness for making musical instruments.
Woody fiber is not properly formed unless the leaves of plants are well exposed to the light. There is no doubt that the cambium (q.v.) performs an important part iu the formation of wood. There has been much difference of opinion among vegetable physi ologists, however, as to the mode of its formation. Two principal theories have long had and still have their advocates—the horizontal and vertical theories. According to the former—supported by Duhamel, Decandolle, Schleiden, Mirbel, Naudin, Henfrey, etc. —the wood of trees is formed by horizontal extension from the stem or from the bark, or from both, for there is much diversity of opinion as to these particulars. According to the latter—supported by Knight, Petit-Thouars, Gaudichaud, Lindley, etc.—the wood is developed in a vertical direction from the leaves, every bud being, as the elder Darwin long ago maintained, an embryo plant sending leaves upward and roots downward.
Wood is not only valuable as timber (q.v.), but for fuel, being the chief fuel used in many parts of the world. To woody fiber we are indebted also for great part of our cordage and textile fabrics, including the very finest of them, as muslin and lace. Reduced to pulp, it is used for the manufacture of paper.
A kind of factitious or artificial wood, used for making ornamented articles, has recently been invented in France. It is called boil dare. It is formed of sawdust, heated to a high temperature, and subjected to very great pressure. Its compactness and hardness exceed those of wood itself. Another kind is made by mixing blood with i sawdust, and compressing. Some kinds of costly wood are also imitated by mixing their sawdust with glue, and casting the mixture into the desired shape in molds.