Wood and Forest. William Noyes

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СКАЧАТЬ trees.

      Under the division of naked-seeded plants (gymnosperms), practically the only valuable timber-bearing plants are the needle-leaved trees or the conifers, including such trees as the pines, cedars, spruces, firs, etc. Their wood grows rapidly in concentric annual rings, like that of the broad-leaved trees; is easily worked, and is more widely used than the wood of any other class of trees.

      Of fruit-bearing trees (angiosperms), there are two classes, those that have one seed-leaf as they germinate, and those that have two seed-leaves.

      The one seed-leaf plants (monocotyledons) include the grasses, lilies, bananas, palms, etc. Of these there are only a few that reach the dimensions of trees. They are strikingly distinguished by the structure of their stems. They have no cambium layer and no distinct bark and pith; they have unbranched stems, which as a rule do not increase in diameter after the first stages of growth, but grow only terminally. Instead of having concentric annual rings and thus growing larger year by year, the woody tissue grows here and there thru the stem, but mostly crowded together toward the outer surfaces. Even where there is radial growth, as in yucca, the structure is not in annual rings, but irregular. These one seed-leaf trees (monocotyledons) are not of much economic value as lumber, being used chiefly "in the round," and to some extent for veneers and inlays; e. g., cocoanut-palm and porcupine wood are so used.

      The most useful of the monocotyledons, or endogens, ("inside growers," as they are sometimes called,) are the bamboos, which are giant members of the group of grasses, Fig. 1. They grow in dense forests, some varieties often 70 feet high and 6 inches in diameter, shooting up their entire height in a single season. Bamboo is very highly valued in the Orient, where it is used for masts, for house rafters, and other building purposes, for gutters and water-pipes and in countless other ways. It is twice as strong as any of our woods.

      Under the fruit-bearing trees (angiosperms), timber trees are chiefly found among those that have two seed-leaves (the dicotyledons) and include the great mass of broad-leaved or deciduous trees such as chestnut, oak, ash and maple. It is to these and to the conifers that our principal attention will be given, since they constitute the bulk of the wood in common use.

      The timber-bearing trees, then, are the:

      (1) Conifers, the needle-leaved, naked-seeded trees, such as pine, cedar, etc. Fig. 45, p. 199.

      (2) Endogens, which have one seed-leaf, such as bamboos, Fig. 1.

      (3) Broad-leaved trees, having two seed-leaves, such as oak, beech, and elm. Fig. 48, p. 203.

      The common classifications of trees are quite inaccurate. Many of the so-called deciduous (Latin, deciduus, falling off) trees are evergreen, such as holly, and, in the south, live oak, magnolia and cherry. So, too, some of the alleged "evergreens," like bald cypress and tamarack, shed their leaves annually.

      

      Fig. 1. A Bamboo Grove, Kioto, Japan.

      

      Fig. 2. Ginko Leaf.

      Not all of the "conifers" bear cones. For example, the juniper bears a berry. The ginko, Fig. 2, tho classed among the "conifers," the "evergreens," and the "needle-leaf" trees, bears no cones, has broad leaves and is deciduous. It has an especial interest as being the sole survivor of many species which grew abundantly in the carboniferous age.

      Also, the terms used by lumbermen, "hard woods" for broad-leaved trees and "soft woods" for conifers, are still less exact, for the wood of some broad-leaved trees, as bass and poplar, is much softer than that of some conifers, as Georgia pine and lignum vitae.

      Another classification commonly made is that of "endogens" (inside growers) including bamboos, palms, etc., and exogens (outside growers) which would include both conifers and broad-leaved trees.

      One reason why so many classifications have come into use is that none of them is quite accurate. A better one will be explained later. See p. 23.

      As in the study of all woods three sections are made, it is well at the outset to understand clearly what these are.

      The sections of a tree made for its study are (Fig. 3):

      (1) Transverse, a plane at right angles to the organic axis.

      (2) Radial, a longitudinal plane, including the organic axis.

      Fig. 3.

A.	B.
A, B, C, D, Transverse Section. B, D, E, F, Radial Section. G, H, I, J, Tangential Section.	A, B, C, Transverse Section. A, B, D, E, Radial Section. B, C, E, F, Tangential Section.

      

      (3) Tangential, a longitudinal plane not including the organic axis.

      If a transverse section of the trunk of a conifer or of a broad-leaved tree is made, it is to be noted that it consists of several distinct parts. See Fig. 4. These, beginning at the outside, are:

       (1) Rind or bark(a) Cortex(b) Bast

       (2) Cambium

       (3) Wood(a) Sap-wood(b) Heart-wood

       (4) Pith.

      Fig. 4. Diagram of Cross-section of Three Year Old Stem of Basswood.

      (1) The rind or bark is made up of two layers, the outer of which, the "cortex," is corky and usually scales or pulls off easily; while the inner one is a fibrous coat called "bast" or "phloem." Together they form a cone, widest, thickest, and roughest at the base and becoming narrower toward the top of the tree. The cortex or outer bark serves to protect the stem of the tree from extremes of heat and cold, from atmospheric changes, and from the browsing of animals. It is made up of a tough water-proof layer of cork which has taken the place of the tender skin or "epidermis" of the twig. Because it is water-proof the outside tissue is cut off from the water supply of the tree, and so dries up and peels off, a mass of dead matter. The cork and the dead stuff together are called the bark. As we shall see later, the cork grows from the inside, being formed in the inner layers of the cortex, the outer layers of dry bark being thus successively cut off.

      The characteristics of the tree bark are due to the positions and kinds of tissue of these new layers of cork. Each tree has its own kind of bark, and the bark of some is so characteristic as to make the tree easily recognizable.

      

      Bark may be classified according to formation and method of separation, as scale bark, which detaches from the tree in plates, as in the willows; СКАЧАТЬ