386 VEGETABLE lEEITABILITT. 



There are thus spiral-twiners, leaf-climbers, tendril-bearers, and 

 hook and root climbers. The most interesting point in the natural 

 history of climbing plants is their diverse powers of movement. The 

 young shoots of the hop revolve during the day and in hot weather, at 

 the rate of two hours and eight minutes for each revolution. The 

 greater number of twiners revolve in a course opposed to that of the 

 sun, or the hands of a watch. The majority therefore ascend the 

 supports from right to left. 



Plants belonging to eight families have clasping petioles, and plants 

 belonging to four families climb by the tips of their leaves. As regards 

 tendrils, they place themselves in the proper position for action, stand- 

 ing, for instance in Cobsea, vertically upwards, and with their branches 

 divergent, and their hooks turned outwards ; or, as in Clematis, the 

 young leaves temporarily curve themselves downwards so as to serve 

 as grapnels. If the young shoot of a twining plant or of a tendril be 

 placed in an inclined position it soon bends upwards, though com- 

 pletely secluded from the light, the guiding stimulus in this case being 

 the attraction of gravity. CKmbing plants bend towards the light by a 

 process closely analogous to that incurvation which causes them to 

 revolve. In some cases the spontaneous revolving movement depends 

 on no outward stimulus, but is contingent on the youth of the part, 

 and on its vigorous health. Sometimes the movement depends on 

 contact with any body. After clasping a support tendrils contract 

 spirally. 



Blondeau and others have shown that ether acts as an anaesthetic 

 on sensitive plants. A current of electricity causes the leaves to fold 

 and the petioles to droop. If too long continued the plant is destroyed. 

 The current could be passed for five or ten minutes without destroying 

 the plant, but when the current lasted for twenty-five minutes the 

 plant was killed. For the effects of ansesthetic agents (such as chloro- 

 form) on plants, see Livingstone's paper in Edin. N. Phil. Journal, 

 2d ser. xi. 333 ; and Mr. W. Coldstream's paper in the same Journal, 

 xiii. 87. 



Movements take place in some parts of the flower, occasionally 

 with the view of scattering the poUen. The stamens of various 

 species of Berberis and Mahonia are articulated to the torus or thalor 

 mus, and when touched at their inner and lower part, move towards the 

 pistil. In Parnassia palustris the stamens move towards the pistil in 

 succession to discharge their contents (fig. 514, p. 286). The common 

 Eock-rose (Helianthemum vulgare) exhibits staminal movements also 

 connected with the bursting of the anthers. Morren has noticed 

 sensitiveness in the andrcecium of Sparmannia africana and Cereus 

 grandiflorus. In the Nettle, Pellitory, Pilea serpyUifolia (the artil- 

 lery plant), and Kalmia, the filaments are confined by the perianth, 

 and are afterwards released so as to allow their elasticity to come into 



