Popular Science Monthly/Volume 49/October 1896/The Significance of Leaves

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WHILE we admire and enjoy the greenness and the general effect of foliage, and regard the forms of single trees if they are particularly graceful or otherwise peculiar in shape, we seldom give special attention to individual leaves, but are rather inclined to neglect them as common and trivial. Yet, as Mr. F. Schuyler Mathews[1] well says, while they may be common, "they are far from commonplace. If we doubt this, let us try to draw or paint a single leaf. Only a great artist can depict all of some one of its manifold truths; one may draw ever so carefully and

Fig. 1.—White Pine, Leaf at A.

well, yet he can not tell with the pencil or the brush all the truth and beauty of one leaf. Its color is too waxen and pure to be imitated by earthy pigments; its outline is too subtile, its teeth are too finely and vigorously formed, and its veins are too infinitely complex for one to copy with absolute, lifelike accuracy. No, it is not possible to portray all the beauty of a leaf with the pencil. Yet this work of Nature's wonderful art is common: the world is filled with untold billions of leaves, no two of which are exactly alike. "It is undoubtedly the fact that we do not fully appreciate either the beauty or the usefulness of trees; but after

Fig. 2.—Catalpa Leaf.

we have become really familiar with them, and have learned readily to distinguish the different species, we find ourselves in a new world of absorbing interest, in which beauty and use have expanded to proportions far beyond our previous conceptions."

Many pleasant and profitable lessons can be learned from Mr. Mathews's two hundred and odd sketches of leaves taken from Nature, with their accompanying brief descriptions. The single lesson to which we would here call attention is the variety in the forms of leaves. The purpose and condition of the life of the tree are revealed in no small measure by its leaves.

The needle of the pine enables the tree to withstand a hurricane on a mountain top, yet its slender figure is perfectly adapted to the task of gathering light and air for the tree's life.

Not less plainly does the diversity of character in a leaf reveal the diversity of tree life itself. No two leaves are exactly alike; no two trees are exactly alike. There are specific as well as generic differences which are strongly marked. One tree leads a rugged, wild, and struggling life; another an easy, luxurious life. The rough and fuzzy leaf of the slippery elm, the silky leaf of the beech, the shiny leaf of the gray birch, these are all widely different; but there are also distinct differences between the leaves of the several kinds of birches, elms, and maples.

Still, there are puzzling similarities, and one is often compelled to study minute details in order to make sure of a particular species. The catalpa leaf is mentioned as that having the simplest form. It is without divisions, and has an entire and unbroken edge. The magnolia leaf, which is oval, might as well have been

Fig. 3.—White Oak.

taken as the type; and there are others equally simple. The most complex form of leaf is exemplified in that of the horse-chestnut.

A very interesting exercise may he had in tracing the differences in the shapes of the leaves of trees of the same family, as of the oaks, where we have the rounded lobed leaf of the white oak, the pointed lobed red-oak leaf, and the obovate, evergreen leaf of the red oak, with numerous transitional and derivative shapes. In the maples, too, the typical three-lobed, deeply indented leaf branches out into a great diversity of forms, all easily referable, however, to the primitive one, the peculiarities of which are dependent upon the depth, the number, and the minuteness of the notchings. Another series of sports is shown in

Fig. 4.—Red Oak. Fig. 5.—Live Oak.

the birch leaves, where the pointed, serrated leaves of the black and yellow birch are quite different in shape and general appearance from the pointed, much-notched, glossy, isosceles-triangled leaves of the white birch. This tree has other marked characteristics. "Notice the bough where it joins the white trunk; this triangular brown patch below the branch is always present in any tree of any age. The leaf stem is slender, rather long, and not downy; the leaf (often growing, as in my sketch, in pairs) is very smooth and shiny on both sides; also, the stem being slender the leaf shakes with the slightest breeze, and its varnished surface, reflecting the sunlight, breaks it into shifting, sparkling green fire."

Another series of sports may be studied in the leaves of the same tree, as the sassafras, of which three plainly marked shapes may be found on the same twig, and the mulberry similarly characterized. A peculiarity of opposite style is presented in the leaf of the tulip tree, which is unique in shape, being cut off at the Fig. 6.—Red Mulberry. end and having a marked hollow or notch where nearly every other leaf is angular or convex.

Our space is filled, and we have said nothing of the pinnate leaves, or the spiny leaves, or the leaves of the spruces and firs, of all of which as interesting studies might be made.

The greatest sphere of usefulness which a tree occupies, Mr. Mathews says, is connected with its life. It is a great air purifier; it absorbs from the atmosphere the carbonic-acid gas which is poisonous to us; it holds and slowly dispenses moisture which the parched air needs; it gives out the ozone (or oxygen in an active electronegative condition) which is peculiarly conducive to our health; and it modifies heat which would otherwise be overpowering. Each leaf is a builder up and an air regulator of a nature which is beneficial to us. "Its capacity for heat and sunshine is something astonishing. I have estimated that a certain sugar maple of large proportions, which grows near my cottage, puts forth in one season about four hundred and thirty-two thousand leaves; these leaves combined present a surface to sunlight of about twenty-one thousand six hundred square feet, or an area equal to pretty nearly half an acre. Every inch of this expanse breathes in life for the tree, and out health for man, while it absorbs in the aggregate an enormous amount of heat and sunlight. In time of rain it also holds the moisture, and allows it to evaporate by slow degrees when hot days return. The forests are vast sponges, which, through the agency of leaves, soak up the beneficent raindrops and compel them to pass slowly through shaded channels to the parched lands beyond. It is indeed quite impossible to overestimate the value

Fig. 7.—Tulip Tree.

of the billions and billions of leaves which work and build for the benefit of humanity."

M. Berthelot reports to the French Academy of Sciences that the subscriptions for the proposed monument to Lavoisier, taken in France and other countries, amount to 47,353 francs, or $9,410. Of this sum, $100 are credited to the United States, The subscription is still open, and considerable sums are expected from particular sources, as the French Department of Public Instruction and the city of Paris; and the Emperor of Russia has headed a subscription list to be opened in his dominions.
  1. Familiar Trees and their Leaves. By F. Schuyler Mathews. With an Introduction by Prof. L. H. Bailey. Published by D. Appleton & Co.