Page:Popular Science Monthly Volume 12.djvu/690

670 notched at the base, so that the lobes of one leaf lap over or lie upon the lobes of the other, thus appearing at first sight, by deception, like the perfoliate leaves on the upper part of a honeysuckle. Each leaf, too, has its upper and its lower plane, the upper one being exposed to the sunlight, and the under one being kept in the shade. The two sides of the leaf differ physiologically, as the stomata, or breathing organs, are on the under side of the leaf. The leaves, too, of the young eucalypt are bright, grassy green; they are also thin, and the tissue soft and somewhat succulent.

Now, not one of these particulars is carried into the maturity of the tree. Perhaps, in its enlarged arboreal wisdom, the big gum-tree eschews them all as the indiscretions of its youth. So the labiate character, or four-sidedness, gives place to a round stem. The leaves are now not amplexicaul, but stand well out from the branch-stems, and sometimes even hang suspended. They have now long petioles, or leaf-stems. In fact, as against the former sessile character of the leaf, the difference is almost forced to the point of exaggeration, since in E. globulus the long-lanceolate leaf seems really an extension and expansion of the petiole, or leaf-stalk. The leaves are no longer opposite, but alternate, nor are they heart-shaped, but long-lanceolate, and often even falcate, or scythe-shaped. Their color is now not grass green, but bluish-green, and the points are tipped with red. The tissue, too, is changed, for the leaves are thick, and leathery, and dry. Nor has the leaf now its sunny side and its shady side distinct—that is, the blade has no upper or lower plane, but an upper and a lower edge, the one edge being set toward the sky and the other toward the earth, thus exposing both planes equally to the sunlight. To accomplish this eccentric adjustment of the leaf, the petiole actually twists itself, as if it really knew what it was about—with, however, seemingly some of that discomfort which attends on strained etiquette. Often the twist or contortion is so evident as to arrest the attention at once; and the amount of torsion is wonderful when it is mentioned that the petiole seems to delight in holding the scythe-shaped leaf with its concave edge uppermost (Fig. 3). It is surely curious to find in the leaves of the adult tree the texture so different from that of the leaves of its youth. But the leaf is now the seat of a much greater physiological change. The two planes of the leaf are now virtually alike—the same in texture and in organs. The ribs and veins are the same, alike prominent on each side, much as if the roof of a house should have its beams and rafters inside and out. And two series of stomata, or breathing-organs, now appear—one series for each side of the leaf. Here, we think, lies much of the secret of the great draining capacity of the eucalypts. Both sides of the leaf work equally. It is as the double-cylinder engine against the single one. It is asserted of the gum-tree that it can eliminate from a swampy soil eight times its own weight of water in twenty-four hours.