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.

(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; membraneous bark, which comes off in ribbons and films, as in the birches; fibrous bark, which is in the form of stiff threads, as in the grape vine; and fissured bark, which breaks up in longitudinal fissures, showing ridges, grooves and broad, angular patches, as in oak, chestnut and locust. The last is the commonest form of bark.

The bark of certain kinds of trees, as cherry and birch, has peculiar markings which consist of oblong raised spots or marks, especially on the young branches. These are called lenticels (Latin lenticula, freckle), and have two purposes: they admit air to the internal tissues, as it were for breathing, and they also emit water vapor. These lenticels are to be found on all trees, even where the bark is very thick, as old oaks and chestnuts, but in these the lenticels are in the bottoms of the deep cracks. There is a great difference in the inflammability of bark, some, like that of the big trees of California, Fig. 54, p. 208, which is often two feet thick, being practically incombustible, and hence serving to protect the tree; while some bark, as canoe birch, is laden with an oil which burns furiously.