Climbing Plants 241 



feels the pressure and begins to curve. Darwin 

 experimented upon one species of clematis with a 



FIG. 67. Scaling-hooks of the Virginia creeper (Ampelopsis quin- 

 quefolia) and of the wild clematis (Clematis Virginiana). 



stick placed so as to press lightly against one of 

 its young leaf-stalks. He found that the leaf-stalk 



