CLIMBERS, PARASITES, SAPROPHYTES. 



199 



circle. In which direction does the shoot revolve with the hands of 

 a watch l or in the opposite direction ? 



(6) We know that warmth hastens the rate of growth of plants : 

 does it hasten the rate of revolution of a twining stem ? Compare the 

 times taken by the same plant to make a complete revolution when 

 kept first in a warm place and then in a cool place, and vice versa. 

 At 33 C. a Runner revolved in 2 hours 20 minutes, while at 23 C. ifc 

 took 3 hours 25 minutes. 



Get several vigorous seedlings ready, each in its own pot. 



Fig. 63. Twining Plants: I., Convolvulus; II., Hop. 



(c) In one pot set a long stick in a vertical position near the plant. 

 Note that the stem swings round and stops at the point where it 

 touches the stick, while its free end goes on revolving ; in this way it 

 finds a support and then goes on growing upwards. 



(d) Must the support be vertical? Try setting the stick in an 

 inclined position, in one pot at 30 from the vertical, in another at 45, 

 and so on. The Runner, like most other twiners, cannot climb up ? 

 stick set at a lower angle than 45 from the vertical. The Convolvulus, 

 however, will twine around a horizontal stick. 



1 The terms "with the sun" and "against the sun" are sometimes 

 used instead of "clockwise" and "anti-clockwise." The plant (placed 

 between sun and observer) points successively to East, South, and 

 West in revolving "with the sun"; this occurs in the Hop and 

 Honeysuckle. The plant points successively to West, South, and 

 East in going "against the sun," i.e. in the anti-clockwise direction 

 this occurs in most climbers, e.g. Scarlet Runner, Convolvulus. 



