General Introduction 21 



instances of sensation in plants. Few conclusive results, 

 however, attended the desultory researches carried out 

 before 1860. The mode of regarding the whole problem 

 gradually underwent a change after the appearance of 

 Darwin's work. The phenomena observed were held to be 

 of interest chiefly as helping to explain certain movements 

 of plants, which nevertheless remained to some extent 

 meaningless. Movement was thought to be the principal 

 subject for investigation in this direction, and irritability 

 was studied for the most part only in its bearing upon 

 movement. This idea by somewhat slow degrees gave 

 way to a broader view, and sensitivity, or the power of 

 appreciating changes in the environment was ascertained 

 to play a far wider part than the causation of movement 

 to be indeed the clue to many so far obscure changes in the 

 interior of plants, which had hardly received observation 

 or recognition. 



Later in the century arose a development ot physiology 

 which now bids fair to assume a very high degree of impor- 

 tance. The study of the individual plant gave way to 

 some extent to the investigation of the mutual relations 

 of plants growing together in some kind of association, 

 and to the study of the vegetation of some particular 

 environment as a whole. This was a departure at once 

 novel and fascinating. It attracted the attention of many 

 of the younger school of botanists and was pursued with 

 much diligence under the name of oecology. Many of the 

 more obscure problems of physiology needed approaching 

 from this standpoint. 



One of the most interesting results of this new field of 

 inquiry was the demonstration of the fact that the main 

 differences between animals and plants are attributable 

 to the one being incapable of movement from place to place, 

 while the other is constructed with a view to locomotion. 



Another very important development of the physio- 



