418 



MOVEMENTS. 



Sicj-os, a curvature soon takes place in the direction of the eon- 

 tact. If the plant is in a vigorous condition and the tendiil is 

 30ung, a slight touch is generalh- snfHcient to cause immediate 

 flexion. If a solid object, for instance a staff, is placed in con- 

 tact with such a tendril, the bending and coiling takes place at 

 once, and thus the organ is brought into close apposition with 

 the support. 



1081. As soon as the tendril has coiled around its support, a 

 striking phenomenon is observed in the portion between the shoot 

 and the support : it begins to twist, throwing the whole thread 

 into a double coil, a part of which winds one way and the 

 rest another. There can be no doubt that this comes from the 

 action of the same force which causes the revolution in the ten- 

 dril before it becomes attached to the support, and the further 

 exercise of this force must necessarily produce two coils running 



in opposite directions. After the tendril has made fast to its 

 suppoi-t, its structure begins to change in a remarkable manner, 

 becoming much firmer and more elastic than before, — a provision 

 adapting it admirably to resist sudden strains upon the main 

 shoot from gusts of wind. 



1082. But if the tendril in its revolution has failed to come in 

 contact with anj' proper support, it is thrown into a single coil, 

 which runs from the extremity of the tendril, and extends for 

 a short distance, perhaps half the whole length of the organ. 

 Sometimes, however, it simply becomes flaccid. 



FlO. 188. Ampelopsis quinqnefolia, or Virginia creeper. 



