834 THE ORIGIN OF SPECIES 



have thus become twiners, they must have independently 

 acquired it, and cannot have inherited it from a common 

 progenitor. Ilence I was led to predict that 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 revolved slightly 

 and irregularly, like the stems of twining plants, but 

 without making any use of this habit. Soon afterward 

 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 utilized 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 spe- 

 cies, belonging to widely distinct groups, are endowed 

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



