Page:Darwin - On the movements and habits of climbing plants.djvu/60

 On one occasion, when a tendril had curled round a small stick, half an inch in diameter, an adhesive disk was formed; but generally the tendrils can do nothing with smooth sticks or posts. If, however, the tip of any one branch can curl round the minutest projecting point, the other branches will form disks, especially if they can find crevices to crawl into. The tendril quite fails to attach itself to a brick wall.

I infer that the disks or balls secrete some resinous adhesive matter, from the adherence of the fibres to them, but more especially from such fibres becoming loose after immersion in sulphuric ether, which likewise removes small, brown, glistening points that can generally be seen on the surface of the older disks. If the hooked extremities of the tendrils touch nothing, the cellular outgrowth, as far as I have seen, never commences; but temporary contact during a moderate time causes small disks to be formed. I have seen eight disks developed on one tendril. After the development of the disks, the tendrils, which now become spirally contracted, likewise become woody and very strong. A tendril in this state supported nearly seven ounces, and would apparently have supported a considerably greater weight had not the fibres of flax to which the disks were attached yielded.

From the facts above given, I infer that though the tendrils of this Bignonia can occasionally adhere to smooth cylindrical sticks and often to rugged bark, yet that they are specially adapted to climb trees clothed with lichens, mosses, or with Polypodium incanum, which I hear from Professor Asa Gray is the case with the forest-trees where this Bignonia grows. Finally, it is a highly remarkable fact that a leaf should become metamorphosed into a branched organ which turns from the light, and which can by its extremities either crawl like roots into crevices, or seize hold of minute projecting points, these extremities subsequently forming cellular masses which envelope by their growth the finest fibres and secrete an adhesive cement.

Eccremocarpus scaber (Bignoniaceæ).—Plants in the greenhouse, though growing pretty well, showed no spontaneous movements in their shoots or tendrils; but, removed to the hot-house, the young internodes revolved at rates varying from 3 h. 15 m. to 1 h. 13 m.: at this latter unusually quick rate one large circle was swept; but generally the circles or ellipses were small, and sometimes the course pursued was extremely irregular. An internode which had made several revolutions would sometimes stand