Ch. Ill, 9] SPECIAL FUNCTIONS OF LEAVES 



77 



simplest case, the petiole acts as the tendril, making a 

 turn around the support, as in our common wild Clematis 

 (Fig. 51). In other cases, as illustrated by our figures, the 

 tendril is a trans- 

 formed leaflet or 

 leaflets, or else 

 stipule-like struc- 

 tures, or even the 

 entire blade. The 

 typical tendril 

 moves about 

 through the air 

 until it touches 

 some object ; then 

 it bends towards 

 the touched side, 

 and, if the object 

 be of suitable form, 

 continues the pro- 

 cess, and makes 

 several turns 

 around it (Fig. 

 52). Then the in- 

 termediate part of 

 the tendril be- 

 comes twisted to 

 a double spiral, 

 drawing the plant 



Closer to the SUp- FlQ 50 — Venus Fly-trap, Dion&a muscipula, a 

 port after which plant which catches insects by sudden closure of its 

 i i v leaf blades; X i. (From Figurier.) 



it develops tough 



fibrous tissues, thus forming a strong but elastic bond be- 

 tween plant and support. In this definite action of tendrils 

 we have another instance of those automatic self -adjustments 

 made possible by the irritability of protoplasm (pages 39, 

 55), this particular form being called thigmotropism. 



