Trees of the Northern United States. A. C. Apgar
White and the Black Oaks.
In the woody portion radiating lines may be seen; these are the silver grain; they are called by the botanist medullary rays.
The central portion of the wood of many large stems is darker in color than the rest. This darker portion is dead wood, and is called heart-wood; the outer portion, called sap-wood, is used in carrying the sap during the growing season. The heart-wood of the Walnut-tree is very dark brown; that of the Cherry, light red; and that of the Holly, white and ivory-like. The heart-wood is the valuable part for lumber.
If examined under a magnifying glass, the annual layers will be seen to consist of minute tubes or cells. In most trees these tubes are much larger in the portion that grew early in the season, while the wood seems almost solid near the close of the annual layer; this is especially true in the Ashes and the Chestnut; some trees, however, show but little change in the size of the cells, the Beech being a good example. In a cross-section, the age of such trees as the Chestnut can readily be estimated, while in the Beech it is quite difficult to do this. Boxwood, changing least in the character of its structure, is the one always used for first-grade wood-engravings.
When wood is cut in the direction of the silver grain, or cut "quartering" as it is called by the lumbermen, the surface shows this cellular material spread out in strange blotches characteristic of the different kinds of wood. Fig. 16 shows an Oak where the blotches of medullary rays are large. In the Beech the blotches are smaller; in the Elm quite small. Lumber cut carefully in this way is said to be "quartered," and with most species its beauty is thereby much increased.
Any one who studies the matter carefully can become acquainted with all the useful and ornamental woods used in a region; the differences in the color of the heart-wood, the character of the annual layers, and the size and the distribution of the medullary rays, afford enough peculiarities to distinguish any one from all others.
Branching.—The regular place from which a branch grows is the axil of a leaf, from what is called an axillary bud; but branches cannot grow in the axils of all leaves. A tree with opposite leaves occasionally has opposite branches; while a tree with alternate leaves has all its branches alternate.
Most branches continue their growth year after year by the development of a bud at the end, called a terminal bud. Many trees form this bud for the next year's growth so early in the year that it is seldom or never killed by the winter weather; such trees grow very regularly and are symmetrical in form. Most evergreens are good examples. Fig. 3 represents a good specimen. The age of such trees, if not too great, can be readily ascertained by the regularity of each year's growth. The tree represented is sixteen years old. The branches that started the fifth year, about the age at which regular growth begins, are shown by their scars on the trunk.
Fig. 3.
The terminal buds of many trees are frequently killed by the frosts of winter; such trees continue their growth by the development of axillary buds; but as growth from an axillary bud instead of a terminal one will make a branch crooked, such trees are irregular in their branching and outline. Just which axillary buds are most apt to grow depends upon the kind of tree, but trees of the same variety are nearly uniform in this respect. Most trees are therefore readily recognized by the form of outline and the characteristic branching. A good example of a tree of very irregular growth is the Catalpa (Indian Bean), shown in Fig. 4. The tendency to grow irregularly usually increases with age. The Buttonwood, for example, grows quite regularly until it reaches the age of thirty to forty years; then its new branches grow in peculiarly irregular ways. The twigs of a very old and a young Apple-tree illustrate this change which age produces.
Fig. 4.
There are great differences in the color and surface of the bark of the twigs of different species of trees; some are green (Sassafras), some red (Peach, on the sunny side), some purple (Cherry). Some are smooth and dotless, some marked with dots (Birch), some roughened with corky ridges (Sweet Gum), etc.
The taste and odor of the bark are characteristics worthy of notice: the strong, fragrant odor of the Spice-bush; the fetid odor of the Papaw; the aromatic taste of the Sweet Birch; the bitter taste of the Peach; the mucilaginous Slippery Elm; the strong-scented, resinous, aromatic Walnut, etc.
The branches of trees vary greatly in the thickness of their tips and in their tendency to grow erect, horizontal, or drooping. Thus the delicate spray of the Birches contrasted with the stout twigs of the Ailanthus, or the drooping twigs of the Weeping Willow with the erect growth of the Lombardy Poplar, give contrasts of the strongest character. In the same way, the directions the main branches take in their growth from the trunk form another distinctive feature. Thus the upward sloping branches of the Elm form a striking contrast to the horizontal or downward sloping branches of the Sour Gum, or, better still, to certain varieties of Oaks.
When the main trunk of a tree extends upward through the head to the tip, as in Fig. 3, it is said to be excurrent. When it is soon lost in the division, as in Fig. 4, it is said to be deliquescent.
Chapter III.
Leaves.
Leaves are the lungs of plants. The food taken in by the roots has to pass through the stem to the leaves to be acted upon by the air, before it becomes sap and is fit to be used for the growth of the plant. No portion of a plant is more varied in parts, forms, surface, and duration than the leaf.
No one can become familiar with leaves, and appreciate their beauty and variety, who does not study them upon the plants themselves. This chapter therefore will be devoted mainly to the words needed for leaf description, together with their application.
The Leaf.—In the axil of the whole leaf the bud forms for the growth of a new branch. So by noting the position of the buds, all the parts included in a single leaf can be determined. As a general thing the leaf has but one blade, as in the Chestnut, Apple, Elm, etc.; yet the Horse-chestnut has 7 blades, the Common Locust often has 21, and a single leaf of the Honey-locust occasionally has as many as 300. Figs. 17–58 (Chapter VII.) are all illustrations of single leaves, except Fig. 43, where there are two leaves on a twig. A number of them show the bud by which the fact is determined (Figs. 25, 26, 31, 33, 34, 36, 40, etc.); others show branches which grew from the axillary buds, many of them fruiting branches (Figs. 37, 42, 43, 50, and 54), one (Fig. 51) a thorny branch.
The cone-bearing plants (Figs. 59−67) have only simple leaves. Each piece, no matter how small and scale-like, may have a branch growing from its axil, and so may form a whole leaf. A study of these figures, together with the observation of trees, will soon teach the student what constitutes a leaf.
Fig. 5.
Arrangement.—There are several different ways in which leaves are arranged on trees; the most common plan is the alternate; in this only one leaf occurs at a joint or node on the stem. The next in frequency is the opposite, where two leaves opposite each other are found at the node. A very rare arrangement among trees, though common in other plants, is the whorled, where more than two leaves, regularly arranged around the stem, are found at the node. When a number of leaves are bundled together—a plan not rare among evergreens—they are said to be fasciculated or in fascicles. The term scattered is used where alternate leaves are crowded on the stem. This plan is also common among evergreens.
Fig. 6.
Caution.—In