Page:Darwin - On the movements and habits of climbing plants.djvu/71

 a certain extent, by the movement from the light or towards any dark object; for neither the internodes nor the tendrils have any proper revolving movement. From this latter circumstance, from the slow movements of the tendrils after contact (though their sensitiveness is retained for an unusual length of time), from their simple structure and shortness, this plant shows less perfection in its means of climbing than any other tendril-bearing plant observed by me. Whilst young and only a few inches in height, it does not produce any tendrils; and considering that it grows to only about 8 feet high, that the stem is zigzag, and is furnished, as well as the petioles, with spines, it is surprising that it should be provided with tendrils, comparatively inefficient though they be. The plant might have been left, one would have thought, to climb by the aid of its spines alone, like our brambles. But, then, it belongs to a genus some of the species of which are furnished with much longer tendrils; and we may believe that S. aspera is endowed with these organs solely from being descended from progenitors more highly organized in this respect.

.—Corydalis claviculata.—According to Mohl (S. 43), both the leaves and the extremities of the branches are converted into tendrils. In the specimens examined by me all the tendrils were certainly foliar, and it is hardly credible that the same plant should produce tendrils of such widely different homological natures. Nevertheless, from this statement by Mohl, I have ranked this Corydalis amongst tendril-bearers; if classed exclusively by its foliar tendrils, it would be doubtful whether it ought not to have been placed amongst leaf-climbers, with its allies, Fumaria and Adlumia. A large majority of its so-called tendrils still bear leaflets, though excessively reduced in size; some few of them may be properly designated as tendrils, for they are completely destitute of laminæ or blades. Consequently we here behold a plant in an actual state of transition from a leaf-climber to a tendril-bearer. Whilst the plant is young, only the outer leaves, but when full-grown all the leaves, have their extremities more or less perfectly converted into tendrils. I have examined specimens from one locality alone, viz. Hampshire; and it is not improbable that plants growing under different conditions might have their leaves a little more or less changed into true tendrils.

Whilst the plant is quite young, the first-formed leaves are not modified in any way, but those next formed have their terminal leaflets reduced in size, and soon all the leaves assume the