Page:Darwin - On the movements and habits of climbing plants.djvu/106

 likewise, according to Mohl and Palm, abounds with climbing plants; and, of the tendril-bearing plants examined by me, the most admirably constructed come from this grand continent, namely, the several species of Bignonia, Eccremocarpus, Cobæa, and Ampelopsis.

.—In my introductory remarks, I staled that, besides the great class of twining plants, with the subordinate divisions of leaf-climbers and tendril-bearers, there were hook- and root-climbers. I mention the former only to say that with the few which I have examined, namely, Galium aparine, Rubus australis, and some climbing Roses, there is no spontaneous revolving movement. If indeed they possessed this power, and were capable of twining, such plants would be placed in the previous great class: thus the Hop, which is a twiner, has reflexed hooks as large as those of the Galium; some other twiners have stiff reflexed hairs; Dipladenia has a circle of blunt spines at the base of its leaves; one tendril-bearing plant alone, as far as I have seen, namely, Smilax aspera, is furnished with spines. Some few plants, which apparently depend solely on their hooks, are excellent climbers, as certain Palms in the New and Old Worlds. Even some of the climbing Roses will ascend the walls of a tall house, if covered with a trellis: how this is effected I know not; for the young shoots of one such Rose, when placed in a pot in a window, bent irregularly towards the light during the day and from it during the night, like any other plant; so that it is not easy to understand how the shoots can get under a trellis close to a wall.

.—A good many plants come under this class, and are excellent climbers. One of the most remarkable is the Marcgravia umbellata, which in the tropical forests of South America, as I hear from Mr. Spruce, grows in a curiously flattened manner against the trunks of trees, here and there putting forth claspers (roots), which adhere to the trunk, and, if the latter be slender, completely embrace it. When this plant has climbed to the light, it sends out free and rounded branches, clad with sharp-pointed leaves, wonderfully different in appearance from those borne by the stem, as long as it is adherent. This surprising difference in the leaves I have observed in a plant of M. dubia in my hothouse. Root-climbers, as far as I have seen, namely, the Ivy (Hedera