64 Chapters in Modern Botany CHAP. 



movement very soon acquires its full ordinary velocity. 

 From seven observations made during August on shoots 

 proceeding from a plant which had been cut down, and on 

 another plant during April, the average rate during hot 

 weather and during the day is 2 hours 8 minutes for each 

 revolution ; and none of the revolutions varied much from 

 this rate. The revolving movement continues as long as 

 the plant continues to grow ; but each separate internocle, 

 as it becomes old, ceases to move." 



The characteristic movement is a turning to all sides in 

 succession. In so doing the stem usually becomes twisted 

 upon itself, and perhaps thus gains in strength, as a rope 

 becomes firmer as it is more twisted. The revolutions 

 continue, though not with equal rapidity, during the night 

 as well as during the day ; the orbit described by the tip 

 of the shoot becomes wider and wider as the shoots grow 

 longer, and the chance of meeting with some upright 

 support becomes greater and greater. The shoot is 

 arrested at length by contact with a support, but the free 

 part goes on revolving. "As this continues, higher and 

 higher points are brought into contact with the support 

 and are arrested ; and so onwards to the extremity ; and 

 thus the shoot winds round its support." 



There is a general uniformity in the behaviour of 

 twining plants, but the direction and rate of revolution 

 vary in different kinds. Thus, as we have mentioned, 

 the majority revolve in a direction opposite to that of the 

 hands of a watch, but many follow the sun ; one shoot 

 may make its revolution in little more than an hour, while 

 another may take a whole day. But at present we are 

 chiefly concerned with the general fact that these twiners 

 do move round and round. 



Leaf-climbers are in their behaviour in some respects 

 intermediate between twiners and tendril-bearers. Like 



