Besides the toes or tendrils, the leaf-stalk is sensitive, and acts like that of a regular leaf-climber, wrapping itself round a neighboring object.
In some cases the young leaves have no tendrils at their tips, but clasp with their stalks, and this is a case exactly the reverse of Tropæolum—a tendril-chamber whose young leaves have no tendrils, instead of a leaf-climber whose young climbing organs are not leaves. Thus the close relationship that exists between leaf-and tendril climbers is again illustrated.
This plant also combines the qualities of another class of climbers, namely, twiners, for it can wind spirally round a support as well as a hop or any other true twiner. Another species (B. Tweedyana) also helps to support itself by putting out roots from its stems, which adhere to the stick up which the plant is climbing. So that here are four different methods of climbing—twining, leaf, tendril, and root climbing—which are usually characteristic of different classes of climbing plants, combined in a single species.
Among the Bignonias are found tendrils with various curious kinds of sensitiveness. The tendrils of one species exhibit, in the highest perfection, the power of growing away from light toward darkness, just the opposite to the habit of most plants. A plant, growing in a pot, was placed so that the light came in on one side. One tendril was pointing away from the light, to begin with, and this did not move; but the opposite tendril, which was pointing toward the light, bent right over and became parallel to the first tendril. The pot was then turned round, so that both pointed toward the light, and they both moved over to the other side, and pointed away from the light. In another case, in which a plant, with six tendrils, was placed in a box, open at one side, all six tendrils pointed like so many weathercocks in the wind—all truly toward the darkest corner of the box. These tendrils also showed a curious power of choice. When it was found that they preferred darkness to light, it was tried whether they would seize a blackened glass tube, or a blackened zinc plate. The tendrils curled round both these objects, but soon recoiled and unwound with what, my father says, he can only describe as disgust. A post with very rugged bark was then put near them; twice they touched it for an hour or two, and twice they withdrew; but at last one of the hooked tendrils caught hold of a little projecting point of bark; and now it had found what it wanted. The other branches of the tendril quickly followed it, spreading out, adapting themselves to all the inequalities of the surface, and creeping into all the little crevices and holes in the bark. Finally a remarkable change took place in the tendrils: the tips which had crept into the cracks swelled up into little knobs, and ultimately secreted a sticky cement, by which they were firmly glued into their places. This plan of forming adhesive disks on its tendrils is one which we shall find used
