18 TWINING PLANTS. UaiP. I, 



but took 9 hrs. 30 m. to make one complete spire round 

 a stick ; Aristohehia 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 un- 

 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 Vriea (ibid. p. 324) on this subjeBt. 



