Page:Popular Science Monthly Volume 22.djvu/47

Rh types. Its myrtles, proteazeas, acacias, and gum-trees exhibit most curious forms, and the grasses, ferns, beeches, araucarias, screw-palms, and bananas are represented; while the thorny rattans wind among the thickets so as to form impenetrable copses.

One of the most curious trees of Northwestern Australia is the monkey-bread tree (Adansonia Gregorii), a baobab, which is plainly distinguished from the African baobab (Adansonia digitata), the only species hitherto known, by its short fruit-stalks. The trunk is swollen to a considerable extent, and the tissues are charged with a mucus like that of the mallows, of which the sheep feeding in the region are very fond, and which they find quite refreshing. The tree is remarkable, among its fellow-plants of the sandstone table-land on which it grows, for its habit of shedding its leaves periodically—a peculiarity which is shared by hardly a dozen among all the Australian trees. Associated with this baobab are relatives of other African plants, of the leguminous Erythroplacum, or poison-tree, and the tamarind; and to these may be added an ally of the Indian crow-nut, or nux vomica.

Many of the Australian plants exhibit various aberrations in the form of their leaves, with some of which specimens of their eucalyptus have made us acquainted. The acacias, which are very abundant, and appear in three hundred species, are many of them, as well as some other leguminous plants, distinctly marked from similar plants in Asia, Africa, and America, by having not veined leaves but phyllods, or leaf -like structures, in which the petiole becomes so much developed as to assume the appearance and perform the functions of a leaf.

Another remarkable adaptation of leaf-forms is exemplified in the Brazilian plant called the Bauhinia, the leaves of which are deeply cleft into two lobes, and given a form which is graphically described by the name Unha de boi, "ox-hoof," which the Portuguese give to the plant. At daybreak, the leaves are borne with both lobes spread out horizontally; as the sun rises in the sky, the lobes rise, and are drawn toward each other, till, in the more sensitive species (Bauhinia Braziliensis), they are completely doubled up, with their backs in contact. As the sun goes down, they begin to separate again, growing wider apart as the afternoon advances, till in the evening they appear again spread out level. During the night they again contract and become folded together. Herr Fritz Midler had an opportunity while in Brazil of observing one of these plants at noon, when a part of the leaves were shaded by the tree under which he was resting. Leaves that were quite closed together, or the lobes of which formed an acute angle with each other, spread out as soon as the shadow struck them, and eventually became horizontal, and even appeared to turn their lobes downward. In no other instance, however, did Herr Muller find the upper surface of the lobes of the leaves inclined to each other at a larger angle than 180.