118 



MOVEMENT 



which, apparently for no reason, sloAvly tvdst round so that 

 their apex describes a circle in the course of one and a half 

 to two minutes. Another movement of the plant body is 

 sho^vn by twining stems. The hop, the scarlet runner bean 

 and the convolvulus revolve round sticks or other supports. 



A 



B 



Fig. 38. A, Hop twining with the sun; B, Convolvulus twining 

 against the sun. After Payer. 



Tendrils are another example of movement. They are, as a 

 rule, whip-like organs ^^dth a hooked tip. They revolve in a 

 spiral way, and when the tips come into contact with a support 

 the tendrils will wrap themselves round it. Morphologically 

 a tendril is usually a part of a leaf, but this is by no means 

 always true. But there are other movements which are due 

 to external conditions. 



