670 THE POPULAR SCIENCE MONTHLY. 



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 oppo- 

 site, 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 tis- 

 sue, 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. 



