1 68 THE METHOD OF DARWIN. 



power on which most climbers depend is 

 inherent though undeveloped in almost every 

 plant in the vegetable kingdom." 1 



It will be interesting to try to analyze the 

 conditions under which he made this definite 

 prediction. In his work on climbing plants he 

 showed that the power to climb depends on two 

 quite distinct powers: (i) the power of spon- 

 taneous circumnutation, and (2) sensitiveness to 

 touch, and the consequent bending toward the 

 side touched. 



Without the theory of descent, the question 

 of the origin of the above mentioned sensitive- 

 ness could never have arisen at all. With the 

 theory of descent, and with natural selection as 

 a cause, and a belief in the existence of varia- 

 tions for it to work upon, it might have been 

 possible to infer some general power or tendency 

 in plants as the source of that sensitiveness to 

 touch; but it was not done, and from what has 

 been said elsewhere it is not likely that it 

 would have been done, at least without great 

 difficulty, from a knowledge of the highly 

 specialized effects. Darwin said, " If we in- 

 quire how the petiole of a leaf, or the peduncle 

 of a flower, or a branch, first becomes sensitive, 

 and acquires the power of bending toward the 



1 Journal, p. 117. 



