Page:Darwin - On the movements and habits of climbing plants.djvu/31

 line was generally formed; but one day, in the course of eight hours and three quarters, the figure traced, clearly represented three and a half irregular ellipses, the most perfect one of which was completed in 2 h. 35 m. The two opposite leaves moved quite independently of each other. This movement would aid that of the internodes in bringing the petioles into contact with surrounding objects. I discovered this spontaneous movement too late to be enabled to observe the leaves in all the other species; but from analogy I can hardly doubt that the leaves of at least C. viticella, C. flammula, and C. vitalba move spontaneously; and, judging from C. Sieboldi, this probably is the case with C. montana and C. calycina. I ascertained that the simple leaves of C. glandulosa exhibited no spontaneous revolving movement.

Clematis viticella, var. venosa.—In this and the two following species the power of spirally twining is completely lost, and this seems due to the lessened flexibility of the internodes and to the interference caused by the large size of the leaves. But the revolving movement, though restricted, is not lost. In our present species a young internode, placed in front of a window, made three narrow ellipses, transversely to the light, at an average rate of 2 h. 40 m.; when placed so that the movement was to and from the light, the rate was greatly accelerated and retarded, as in the case of twining plants. The ellipses were small; the longer diameter, described by the apex of a shoot bearing a pair of not expanded leaves, being only 4⅝ inches, and that by the apex of the penultimate internode only 1⅛ inch; at the most favourable period of growth each leaf would hardly be carried to and fro by the movement of the internodes more than two or three inches, but, as above stated, it is probable that the leaves themselves move spontaneously. The movement of the whole shoot by the wind and by its rapid growth would probably be almost equally efficient with the spontaneous movements in bringing the petioles into contact with surrounding objects.

The leaves are of large size. There are three pairs of lateral leaflets and a terminal one, all borne by rather long petioles. The main petiole bends a little angularly downwards at each point where a pair of leaflets arises, and the petiole of the terminal leaflet is bent downwards at right angles; hence the whole petiole, with its rectangularly bent extremity, acts as a hook. This, with the lateral petioles directed a little upwards, forms an excellent grappling apparatus by which the leaves readily become entangled with surrounding objects. If they catch nothing, the