MOVEMENT IN PLANTS. 237 



show the direction in which the stem-tip points ; (2) by using 

 a plumb-line (a string with a weight tied at one end) and 

 marking the spot 011 the paper below the stem-tip ; (3) by 

 fixing a sheet of glass above the plant and marking on it 

 the position of the stem- tip. Whichever plan is used, 



Fig. 54. Twining Plante : I., Convolvulus; II., Hop. 



record the time when each observation is made, and find 

 out how long it takes for the stem-tip to swing round 

 through a complete circle. In which direction does the 

 shoot revolve with the hands of a clock 1 or in the 

 opposite direction ? 



316. Influence of Temperature on Bate of Revolu- 

 tion. Compare the times taken by the same plant to 

 make a complete revolution when kept first in a warm 



1 The terms "with the sun" and "against the sun" are some- 

 times 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 jFig. 54, n.) and Honeysuckle. The plant points succes- 

 sively 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. 



