Outside my window the trees in a little wood stand leafless. Everything which made this wood a delight in June, the contrast of light and shade among the leaves, the varying tones of green in broken sunlight, the warmth and color and summer freshness, has gone, but the trees themselves, in all their wealth of foliage were never so beautiful as now. The massive moulding of their trunks, the graceful curves of their branches, the fine tracery of their little bare twigs, now clear against the sky and again lost in a tangled network of intersecting branches,—the whole beauty of their symmetry, their poise, strength, and delicacy is revealed as it is never revealed in summer.

Attracted first by the obvious grace of the forms of trees as we see them from our windows in winter, we discover that a closer study of the details of bare twigs and buds in the woods discloses unsuspected beauty in texture, form, and color. Each tree has definite traits of its own which distinguish it from every other tree, and by tracing individual characteristics in the branches, trunk, stems, buds, and leaf-scars we are able to identify every tree with certainty.

By observing the shapes and general outlines of trees in winter we are able to recognize them at a distance. This study of tree forms adds much to the pleasure of a railroad journey or a winter’s drive in the country, and accuracy is acquired by constant practice when we walk in the woods and fields and can verify the name of each tree. In this way we become familiar with the common trees, and learn to know the predominating trees of the forests through which we pass, often recognizing a rare species the distance of a field away.

There are two distinct plans of branching in trees. When the main trunk extends upward to the tip, as it does in the larch and other conical trees, it is said to be excurrent, and when the main stem divides into many more or less equal divisions, as we find it in the American elm and other spreading trees, it is said to be deliquescent,—the latter form is the most common one among our deciduous trees.

The inner structure of these dicotyledonous trunks is seen when we examine the cross section cut of a felled tree. In the centre is the heartwood, the durable wood of commercial value, the cells of which are hard and dry; next it the soft sapwood, the living part of the tree containing cells filled with sap; then the cambium layer, the zone of growing cells, and outside of this the bark. Each year new cells are formed in the cambium layer, the inner ones making new wood, the outer ones new bark, and by counting these annual rings of growth the approximate age of the tree is found. In young trees there is a conspicuous central portion of pith which remains after the tree matures, as long as the heartwood is sound. The lines radiating from the centre to the circumference are called medullary or pith rays and form the “silver grain” of the wood. As the size of the trunk increases, the bark unable to expand, cracks in fissures or peels in layers, and is pushed off by the tremendous growing power from within. The heartwood is not a living part of the structure and often trees live for years without it,—hollow shells with a normal amount of vitality so long as the roots, the cambium layer and the buds are not injured.

Branches grow from the axillary or lateral buds on the stem, continuing their growth every year by the development and unfolding of new buds, both terminal and lateral. When the growth is carried on by the terminal buds, the tree is more apt to be regular in outline than when these are injured or killed and lateral buds develop the growth instead. Branches vary in showing an upright, drooping, or horizontal habit of growth, as we see them in the Lombardy poplar, weeping willow and tupelo, and within these divisions there are other contrasts of rigidity and flexibility, with differences of color and texture as well.

Apart from the general shape of the tree, the bark on the trunk and branches is a constant help in identification. It is hard and smooth on some trees, like that of the hornbeam and beech, fissured into ridges like the sugar maple on others, it sometimes flakes off in rough plates like those of the shagbark hickory, and again in thin, brittle strips like those of the hop hornbeam, the bark peels off laterally as in the canoe birch, and occasionally becomes ridged and corky as we find it on the branches of the liquidamber and cork elm. Very often the color of the bark is distinctive as is that of the green stems of the sassafras and moosewood maple and the white, brown, pink, and yellow trunks of different birches. The taste and odor of the bark are also characteristic of certain species, as, for instance, the unpleasant, bitter taste of the black cherry, the mucilaginous taste of the slippery elm, and the aromatic fragrance of the stems of the mockernut hickory. The little dots on young bark are called lenticels, they are openings for admitting air to the inner tissues. Lenticels are conspicuous in the bark of the birches.

The presence of thorns on the trunk and branches of certain trees helps us to distinguish them from others, and the clusters of dry fruit which remain hanging on some trees through the winter are another means of identification.

Stems and twigs vary from the finest, lightest sprays to the most coarsely moulded ones,—from the delicate twigs of the hop hornbeam to the stout shoots of the horsechestnut;—like larger branches their tips either ascend, droop, or grow at right angles from the stem, and may be smooth, downy, or rough to the touch.

The pith in cross sections of twigs shows different forms and is a means in itself of distinguishing some trees. It is usually circular, but in some species it takes the form of a pentagon or a star. In a vertical section we sometimes find it in horizontal plates, like the chambered pith of the walnuts. The color is usually white, but sometimes we find it pink, yellowish, green, red, and brown.

It is interesting to find that the history of a tree for several years past can be told by studying the scars along the bare stems. The annual growth each year is marked by a circle of scars around the stem, which was left by the scales of the buds when they opened in the spring, and these scars mark each season’s growth for successive years along the stem.

Besides these circles of scars, there are scars on each side of the stem which were left by the leaves when they fell in the autumn. These leaf-scars differ distinctly in various species and may be round, narrow, triangular, oval, heart-shaped, or horseshoe-shaped according to the species of the tree. They are either flat upon the stem or on a projection, they are sometimes concave and again convex. They may be opposite each other on the stem, as those of the horsechestnut, maples, and ashes, or the arrangement may be alternate, as that of hickories, walnuts and oaks. The places on the stem where the leaf-scars appear are called nodes, and the spaces between the nodes are called internodes.

Occasionally stipule scars are found on the stems,—inconspicuous scars left by stipules, the leaf-like bodies found at the base of leafstalks on some trees,—and sometimes we find the scars of fruit stalks.

Bundle-scars are the scars of the little fibres, the vascular bundles which fastened the leaves to the stems in summer. They are found on the leaf-scars and usually take their shape more or less. On the large leaf-scars they can be seen clearly, but on delicate twigs where the leaf-scars are small it is well to use a magnifying glass.

In our climate the buds of trees are formed in the summer during the season’s growth. The bud at the tip of the stem is called the terminal bud, the buds in the axils of the leaf-scars are called the axillary or lateral buds. Buds contain complete branches in miniature which develop in the spring into a new crop of twigs. By opening a bud in winter the little leaves can be seen and often a cluster of flowers, packed away from the cold in marvellous warm wrappings.

As a rule the terminal bud carries on the growth of the tree and the lateral buds furnish the side branches. Flowers are found in both terminal and lateral buds, but sometimes they are enclosed in buds by themselves which open before the leaves come out in the spring, like those of the red maple and American elm,—these are called flower buds. Occasionally we find two or three lateral buds together called accessory buds,—superposed, if placed one above another as they are in the butternut; collateral, if side by side as in the red maple. When several buds are crowded together one bud usually remains latent. Latent buds are sometimes caught in the growing bark of the tree and remain undeveloped for years, breaking out at length perhaps up and down the sides of the trunk as we see them in “feathered elms.” These abnormal and irregular buds are called adventitious buds.

The winter buds of trees may be large or small, they may be slender, flat, oval, pointed or round, hidden or exposed, they may be smooth, downy, sticky, or rough, covered with scales or naked, and they may differ in color from pale yellow to an inky black.

From the great outlines of the trees against the sky to the little scales of the buds on the stems we marvel to find here as in all nature, order, law, consistency out of infinite variety.