Chap. VII.] THEOEY OF NATURAL SELECTION. 307 



some slight tendency to a movement of this kind would 

 be found to be far from uncommon with plants which did 

 not climb ; and that this had afforded the basis for natural 

 selection to work on and improve. When I made this 

 prediction, I knew of only one imperfect case ; namely 

 of the young flower-peduncles of a Maurandia which re- 

 volved slightly and irregularly, like the stems of twining 

 plants, but without making any use of this habit. Soon 

 afterwards Fritz Miiller discovered that the young stems 

 of an Alisma and of a Linum, — plants which do not 

 climb and are widely separated in the natural system, 

 — revolved plainly, though irregularly ; and he states 

 that he has reason to suspect that this occurs with some 

 other plants. These slight movements appear to be of 

 no service to the plants in question ; anyhow, they are 

 not of the least use in the way of climbing, which is the 

 point that concerns us. Nevertheless we can see that if 

 the stems of these plants had been flexible, and if under 

 the conditions to which they are exposed it had profited 

 them to ascend to a height, then the habit of slightly 

 and irregularly revolving might have been increased and 

 utilised through natural selection, until they had become 

 converted into well-developed twining species. 



With respect to the sensitiveness of the foot-stalks of 

 the leaves and flowers, and of tendrils, nearly the same 

 remarks are applicable as in the case of the revolving 

 movements of twining plants. As a vast number of 

 species, belonging to widely distinct groups, are endowed 

 with this kind of sensitiveness, it ought to be found in a 

 nascent condition in many plants which have not become 

 climbers. This is the case : I observed that the young 

 flower-peduncles of the above Maurandia curved them- 

 selves a little towards the side which was touched. 



