18 TWINING PLANTS. Cua. L 
but took 9 hrs. 30 m. to make one complete spire round 
a stick ; Aristolochia gigas revolved in about 5 hrs., but 
took 9 hrs. 15 m. to complete its spire. This, I presume, 
is due to the continued disturbance of the impelling 
force by the arrestment of the movement at successive 
points ; and we shall hereafter see that even shaking a 
plant retards the revolving movement. The terminal 
internodes of a long, much-inclined, revolving shoot of 
the Ceropegia, after they had wound round a stick, 
always slipped up it, so as to render the spire more 
open than it was at‘ first; and this was probably in 
part due to the force which caused the revolutions, 
being now almost freed from the constraint of gravity 
and allowed to act freely. With the Wistaria, on the 
other hand, a long horizontal shoot wound itself at 
first into a very close spire, which remained une 
changed; but subsequently, as the shoot twined 
spirally up its support, it made a much more open 
spire. With all the many plants which were allowed 
freely to ascend a support, the terminal internodes 
made at first a close spire; and this, during windy 
weather, served to keep the shoots in close contact 
with their support; but as the penultimate internodes 
grew in length, they pushed themselves up for a 
considerable space (ascertained by coloured marks on 
the shoot and on the support) round the stick, and the 
spire became more open.* 
It follows from this latter fact that the position 
* See Dr. H. de Vries (ibid. p. 324) on this subject. 
