22 TWINING PLANTS. Cuap. 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 Vries, 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. 185), 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 
