CHAP, xi Sensitivity and Stimulation 459 



of irritability, excitability, and sensation, had been recog- 

 nized as an existing factor in the plant's life. Still, its exact 

 importance was not properly realized, for the attention that 

 had been given to the subject was directed rather to the 

 movements or changes of position that were observed to 

 take place as conditions changed. These were put in the 

 place of chief importance ; indeed most of the explanations 

 of movement that were advanced were based upon a direct 

 and mechanical change or series of changes, set up by the 

 conditions in the cells or areas that carry out the move- 

 ments. The idea of a response to the environmental change, 

 carried out by an organ as a whole, to secure some advantage 

 thereby, did not find adequate recognition by the botanists 

 of the time. 



The whole question of phytodynamics, important as it 

 is, had fallen a good deal into the background since the 

 time of Dutrochet. From about 1860 onwards, under the 

 stimulus afforded by a new point of view, it came to occupy 

 a leading place in botanical research at the hands of a new 

 school of workers. 



In this departure considerable importance attaches to 

 the appearance of the Origin of Species. True, the latter 

 dealt with many other problems than these, and directed 

 attention to many questions of morphology as well as 

 physiology. The study of structural adaptations, mechan- 

 isms of pollination, distribution of seeds, and kindred 

 problems, received from it a great impetus. These, how- 

 ever, ultimately meet explanation only or mainly on the lines 

 of the influence brought to bear upon structure by environ- 

 ment, considered in the widest sense. The idea of action and 

 reaction between the organism and its environment, embodied 

 in the struggle for existence, invested the study of phyto- 

 dynamics with an importance that had not been realized 

 by the writers of the earlier period, and under the influence 

 of the new view, researches became more numerous and 



