DEDUCTION. GENERAL INSTANCES. 169 



touched side, we get no certain answer. Nev- 

 ertheless, an observation by Hofmeister well 

 deserves attention, namely, that the shoots and 

 leaves of all plants, whilst young, move after 

 being shaken; and it is almost invariably young 

 petioles and young tendrils, whether formed of 

 modified leaves or flower-peduncles, which move 

 on being touched; so that it would appear as 

 if these plants had utilized and perfected a 

 widely distributed and incipient capacity, which 

 capacity, as far as we can see, is of no service to 

 ordinary plants." l 



Darwin was in search of a source of the sen- 

 sitiveness of plants, and Hofmeister had pro- 

 vided it by empirical observation. Darwin's 

 relation to this explanation was exactly the 

 same as it was in the discovery of the principle 

 of natural selection. It will be seen that in 

 the latter case he had studied very carefully the 

 effects (adaptations) to be accounted for, and 

 variations as the material upon which the un- 

 known cause might act; then by accidental 

 reading of Malthus the cause was presented 

 to him, and he brought it and its effects into 

 relation with each other by interpreting the 

 latter as results of the action of the former. In 

 the case of the sensitiveness to touch in plants, 



1 Journal, p. 112. 



