_Solanum dulcamara_ is one of the feeblest and poorest of twiners: it may often be seen growing as an upright bush, and when growing in the midst of a thicket merely scrambles up between the branches without twining; but when, according to Dutrochet (tom. xix. p. 299), it grows near a thin and flexible support, such as the stem of a nettle, it twines round it. I placed sticks round several plants, and vertically stretched strings close to others, and the strings alone were ascended by twining. The stem twines indifferently to the right or left. Some others species of Solanum, and of another genus, viz. _Habrothamnus_, belonging to the same family, are described in horticultural works as twining plants, but they seem to possess this faculty in a very feeble degree. We may suspect that the species of these two genera have as yet only partially acquired the habit of twining. On the other hand with _Tecoma radicans_, a member of a family abounding with twiners and tendril-bearers, but which climbs, like the ivy, by the aid of rootlets, we may suspect that a former habit of twining has been lost, for the stem exhibited slight irregular movements which could hardly be accounted for by changes in the action of the light. There is no difficulty in understanding how a spirally twining plant could graduate into a simple root-climber; for the young internodes of _Bignonia Tweedyana_ and of _Hoya carnosa_ revolve and twine, but likewise emit rootlets which adhere to any fitting surface, so that the loss of twining would be no great disadvantage and in some respects an advantage to these species, as they would then ascend their supports in a more direct line. {44} CHAPTER II. LEAF-CLIMBERS. Plants which climb by the aid of spontaneously revolving and sensitive petioles—_Clematis_—_Tropæolum_—_Maurandia_, flower-peduncles moving spontaneously and sensitive to a touch—_Rhodochiton_—_Lophospermum_—internodes sensitive—_Solanum_, thickening of the clasped petioles—_Fumaria_—_Adlumia_—Plants which climb by the aid of their produced midribs—_Gloriosa_—_Flagellaria_—_Nepenthes_—Summary on leaf-climbers. WE now come to our second class of climbing plants, namely, those which ascend by the aid of irritable or sensitive organs. For convenience’ sake the plants in this class have been grouped under two sub-divisions, namely, leaf-climbers, or those which retain their leaves in a functional condition, and tendril-bearers. But these sub-divisions graduate into each other, as we shall see under Corydalis and the Gloriosa lily.