Page:Darwin - On the movements and habits of climbing plants.djvu/115

 avoid asking, whether the difference between foliar and axial organs can be of so fundamental a nature as is generally supposed to be the case.

We have attempted to trace some of the stages in the genesis of climbing plants. But, during the endless fluctuations in the conditions of life to which all organic beings have been exposed, it might have been expected that some climbing plants would have lost the habit of climbing. In the cases given of certain South African plants belonging to great twining families, which in certain districts of their native country never twine, but reassume this habit when cultivated in England, we have a case in point. In the leaf-climbing Clematis flammula, and in the tendril-bearing Vine, we see no loss in the power of climbing, but only a remnant of that revolving-power which is indispensable to all twiners, and is so common, as well as so advantageous, to most climbers. In Tecoma radicans, one of the Bignoniaceæ, we see a last and doubtful trace of the revolving-power.

With respect to the abortion of tendrils, certain cultivated varieties of Cucurbita pepo have, according to Naudin, either quite lost these organs or bear semi-monstrous representatives of them. In my limited experience, I have met with only one instance of their natural suppression, namely, in the common Bean. All the other species of Vicia, I believe, bear tendrils; but the Bean is stiff enough to support its own stem, and in this species, at the end of the petiole where a tendril ought to have arisen, a small pointed filament is always present, about a third of an inch in length, and which must be considered as the rudiment of a tendril. This may be the more safely inferred, because I have seen in young unhealthy specimens of true tendril-bearing plants similar rudiments. In the Bean these filaments are variable in shape, as is so frequently the case with all rudimentary organs, being either cylindrical, or foliaceous, or deeply furrowed on the upper surface. It is a rather curious little fact, that many of these filaments when foliaceous have dark-coloured glands on their lower surfaces, like those on the stipules, which secrete a sweet fluid; so that these rudiments have been feebly utilized.

One other analogous case, though hypothetical, is worth giving. Nearly all the species of Lathyrus possess tendrils; but L. nissolia is destitute of them. This plant has leaves, which must have