Page:Darwin - On the movements and habits of climbing plants.djvu/50

 nature together; but I shall treat of each family, one after the other, according to convenience. The species to be described belong to ten families, and will be given in the following order:—Bignoniaceæ, Polemoniaceæ, Leguminosæ, Compositæ, Smilaceæ, Fumariaceæ, Cucurbitaceæ, Vitaceæ, Sapindaceæ, Passifloraceæ.

.—This family contains many tendril-bearers, some twiners, and some root-climbers. The tendrils are always modified leaves. Nine species of Bignonia, selected by hazard, are here described, in order to show what diversity of structure and action there may be in species of the same genus, and to show how remarkable the action of the tendrils may be in some cases. The species, taken together, afford connecting links between twiners, leaf-climbers, tendril-bearers, and root-climbers.

Bignonia (an unnamed species from Kew, closely allied to B. unguis, but with smaller and rather broader leaves).—A young shoot from a cut-down plant made three revolutions against the sun, at an average rate of 2 h. 6 m. The stem is thin and flexible and twined, ascending, from left to right, round a slender vertical stick as perfectly and as regularly as any true twining-plant. When thus ascending, it makes no use of its tendrils or its petioles; but when it twined round a rather thick stick, and its petioles were brought into contact with it, these curved round the stick, showing that they have some degree of irritability. The petioles also exhibit a slight