HABITS OF CLIMBING PLANTS. 167 



covered. When a shoot has remained for a considerable time 

 wound round its support, it permanently retains its spiral 

 form even when the support is removed. 



" When a stick was placed so as to arrest the lower and rigid 

 internodes of the Ceropegia at the distance at first of 15 and 

 then of 21 inches from the centre of revolution, the shoot slowly 

 and gradually slid up the stick, so as to become more and more 

 highly inclined : and then, after an interval sufficient to have 

 allowed of a semi-revolution, it suddenly bounded from the 

 stick and fell over to the opposite side, to its ordinary slight 

 inclination. It now recommenced revolving in its usual 

 course, so that after a semi-revolution it again came into con- 

 tact with the stick, again slid up it, and again bounded from 

 it. This movement of the shoot had a very odd appearance, 

 as if it were disgusted with its failure but resolved to try 

 again. We shall, I think, understand this movement by con- 

 sidering the former illustration of the sapling, in which the 

 contracting surface was supposed to creep from the southern, 

 by the eastern, to the northern, and thence back again by the 

 western side to the southern face, successively bowing the sap- 

 ling in all directions. Now with the Ceropegia, the stick 

 being placed a very little to the east of due south of the plant, 

 the eastern contraction could produce no effect beyond pressing 

 the rigid internode against the stick ; but as soon as the con- 

 traction of the northern face began, it would slowly drag the 

 shoot up the stick ; and then, as soon as the western contrac- 

 tion had well begun, the shoot would be drawn from the stick, 

 and its weight coinciding with the northwestern contraction, 

 would cause it suddenly to fall to the opposite side with its 

 proper slightly inclined positions ; and the ordinary revolving 

 movement would go on. I have described this case because it 

 first made me understand the order in which the contracting 

 or turgescent cells of revolving shoots must act. 



" The view just given further explains, as I believe, a fact 

 observed by Von Mohl (S. 135), namely, that a revolving 

 shoot, though it will twine round an object as thin as a thread, 

 cannot do so round a thick support. I placed some long 

 revolving shoots of a Wistaria close to a post between 5 and 



