22 TWINING PLANTS. Chap. I. 



from the northern by the western to the southern 

 face ; and thence back again by the eastern to the 

 northern face, successively bowing the sapling in all 

 directions. Now with the Ceropegia, the stick being 

 placed to the south of the shoot and in contact with 

 it, as soon as the circulatory growth reached the 

 western surface, no effect would be produced, except that 

 the shoot would be pressed firmly against the stick. 

 But as soon as growth on the southern surface began, 

 the shoot would be slowly dragged with a sliding move- 

 ment up the stick ; and then, as soon as the eastern 

 growth commenced, the shoot would be drawn from the 

 stick, and its weight coinciding with the effects of the 

 changed surface of growth, would cause it suddenly to 

 fall to the opposite side, reassuming its previous slight 

 inclination ; and the ordinary revolving movement 

 would then go on as before. I have described this 

 curious case with some care, because it first led me to 

 understand the order in which, as I then thought, the 

 surfaces contracted ; but in which, as we now know from 

 Sachs and H. de Yries, they grow for a time rapidly, 

 thus causing the shoot to bow towards the opposite 

 side. 



The view just given further explains, as I believe, 

 a fact observed by Mohl (p. 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 6 inches in diameter, 

 but, though aided by me in many ways, they could 



