HABITS OF CLIMBING PLANTS. 171 



angles ; and the curvature was always toward the rubbed 

 side." 



Here, then, is one case in which the sensibility of a stem is 

 manifest, and is turned to useful account. The peduncles of 

 the allied Maurandia semperfiorens are also sensitive and 

 flexuous, although Mr. Darwin insists that they are useless 

 for climbing. That some stems should be sensitive might 

 have been expected ; for tendrils of axial nature (e. gr. of 

 Pasnfiova gracilis) are not less sensitive than those of foliar 

 nature, as of Leguminosce^ Cucurhitaceoi^ and Cobsea. And 

 if twining stems in general are not endowed with " a dull 

 kind of irritability," as Mohl conjectured, it may well be 

 because the equally wonderful automatic revolving movement 

 leaves no need for it. In general, the most striking cases of 

 automatic movement belong to leaves or their homologues. 



The distinction can be only somewhat arbitrarily drawn 

 between Leaf -climbers — especially those with small or un- 

 developed leaflets, or where the tip of the leaf forms a hook 

 or tendril-like projection — and Tendril-climbers. The ten- 

 dril, however, whether answering to leaf or stem, is the more 

 specialized organ, adapted only for climbing, and endowed in 

 different plants with very various and some highly remark- 

 able powers. To this subject Mr. Darwin has devoted more 

 than half of his essay. An analysis of it must be deferred, 

 for want of space. 



Near the close of the essay, under Hook-climbers, Mr. 

 Darwin remarks that : — 



" Even some of the climbing Roses will ascend the walls of 

 a tall house, if covered with a trellis ; how this is effected I 

 know not ; for the young shoots of one such Rose, when 

 placed in a pot in a window, bent irregularly toward the light 

 during the day and from it during the night, like any other 

 plant ; so that it is not easy to understand how the shoots can 

 get under a trellis close to a wall." 



Now we have had occasion to observe that the strong sum- 

 mer-shoots of the Michigan Rose (^Mosa setigera, Mx., R. ruhi- 

 folia^ R. Br.), trained on a latticed wall, are strongly disposed 

 to push into dark crevices and away from the light ; they 



