DEDUCTION. GENERAL INSTANCES. 17 1 



power to revolve had its source in an unknown 

 general tendency, just as sensitiveness to touch 

 had its source in a known slight general sen- 

 sitiveness, each power having been developed 

 and specialized in climbing plants by natural 

 selection? Such an inference would seem al- 

 most inevitable. But in addition he was in 

 actual possession of a case in which the power 

 of revolving was imperfect and functionless. 



He said that when he made the prediction he 

 "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 mak- 

 ing any use of the habit." l In the discussion 

 of Maurandia semperflorens, in his original 

 paper on climbing plants, he gave the follow- 

 ing interesting bit of history : " I should not 

 have noticed the present species, had it not 

 been for the following unique case. Mohl says 

 that the flower-peduncles, as well as the petioles, 

 are wound into tendrils." Darwin proved that 

 the flower-peduncles do not act as tendrils ; but 

 that they nevertheless, whilst young, exhibit 

 feeble revolving powers, and are slightly sen- 

 sitive to a touch. He observed nine vigorous 

 plants, and it was certain to him that neither 



1 Origin of Species, p. 197. 



