Page:Darwin - On the movements and habits of climbing plants.djvu/46

 Corydalis claviculata.—This plant is interesting from being in a condition so exactly intermediate between a leaf-climber and a tendril-bearer that it might have been described under either head; but, for reasons hereafter assigned, it is classed amongst tendril-bearers.

Besides the plants already described, Bignonia unguis and its close allies, though aided by tendrils, as will hereafter be described, have clasping petioles. According to Mohl (S. 40), Cocculus Japonicus (one of the Menispermaceæ) and a fern, the Ophioglossum Japonicum (S. 39), climb by their leaf-stalks.

We now come to a small section of plants which climb by the aid of the produced midribs or tips of their leaves.

.—G. Plantii (Liliaceæ).—The stem of a half-grown plant continually moved, generally describing an irregular spire, but sometimes ovals, with the longer axes running in different directions. It either followed the sun, or moved in an opposite course, and sometimes stood still before reversing its course. One oval was completed in 3 h. 40 m.; of two horseshoe-shaped figures, one was completed in 4 h. 35 m. and the other in 3 h. The tip of the shoot, in its movements, reached points between four and five inches asunder. The young leaves, when first developed, stand up nearly vertically; but by the growth of the axis, and by the spontaneous bending down of the terminal half of the leaf, they soon become much inclined, and ultimately horizontal. The end of the leaf forms a narrow, ribbon-like, thickened projection, which at first is nearly straight; but by the time the leaf has got into an inclined position, the end has bent itself downwards into a well-formed hook; and this is now strong and rigid enough to catch any object, and, when caught, to anchor the plant and stop the revolving movement. This hook is sensitive on its inner surface, but not in nearly so high a degree as with the many before-described petioles; for a loop of string, weighing 1.64 grain, produced no effect. When the hook has caught a thin twig or even a rigid fibre, the point may be perceived in from 1 h. to 3 h. to have curled a little inwards; and, under favourable circumstances, in from 8 h. to 10 h. it finally curls round and seizes the object, which it never again looses. The hook when first formed, before the leaf has become inclined, is less sensitive. The hook, if it catches hold of nothing, remains for a long period open and sensitive; ultimately the tip spontaneously and slowly curls inwards, and makes a button-like, flat, spiral coil at the end of the leaf. One leaf was