CHAPTER XI 



THE DEVELOPMENT OF THE THEORY OF SPECIAL 

 SENSITIVENESS UNDER THE INFLUENCE OF 

 THE ORIGIN OF SPECIES 



The conception of the existence of a close inter-relation- 

 ship between the plant and its environment, and of varied 

 efforts of the plant to adapt itself to changes in the latter, 

 followed very quickly upon the appearance of the Origin 

 of Species, and was gradually brought more and more into 

 prominence during the period under review. Close observa- 

 tion of many phenomena, which escaped examination till 

 the sixties and later, brought out in numberless cases such 

 evidence of purposeful adaptation that the idea became 

 the dominant one in this section of the field of research. 

 It is true that the purpose of a movement or of some less 

 evident change did not always prove easy of interpretation, 

 but failure in certain instances does not diminish the 

 importance of the point of view. 



The recognition of a purposeful change in response to 

 a stimulation led gradually to the coincident recognition 

 of physiological mechanisms, which only slowly became 

 familiar, but which when once appreciated threw great light 

 on certain peculiarities of structure not properly interpreted 

 previously. 



In i860 these ideas were somewhat dimly appreciated. 

 It is true that Dutrochet had made important researches 

 into the influence of light and gravity upon various organs, 

 and that Von Mohl had published his classical essay on 

 tendrils and climbing plants ; true, also, that the property 

 described by de Candolle and by Meyen under the names 



