92 



SOCIAL CONJUNCTIVE SYMBIOSIS 



tendril at the point of contact within a minute or two. Even con- 

 tact with a cotton thread, moved by Hght air currents, has been 

 known to produce a reaction in a tendril. 



The bending of the tendril is brought about through an increase 

 in the rate of growth on the side opposite that stimulated, accom- 

 panied by a decrease in the rate on the side which receives the 

 stimulus. As the tendril bends around the support new regions 

 make contact with it and are stiniylated. Thus the encircling con- 

 tinues until the entire tendril is coiled about the support. Often 



Fig. 38. — Trees covered with Virginia creeper (Psedera quinquefolia) , a root 



climber. 



that part of the tendril between the climbing plant and its supporting 

 host coils into the form of a coil spring. This actually serves as a 

 spring, stretching out and closing again during wind storms in such a 

 way as to greatly diminish the danger of being broken or torn away 

 from the support. 



Tendrils may be formed from very diverse morphological parts 

 of plants but usually they are either leaves or parts of leaves, or 

 branches. In the climbing Troyxoluvi the petioles serve as tendrils 



