viii PLANT RESPONSE 



at that time President, for the facilities which he then afforded 

 me for the full publication of my results in the ' Journal ' of 

 the Linnean Society, and for the warm interest which he has 

 manifested in my work, both then and later. 



I next undertook to demonstrate that all the important 

 characteristics of the responses exhibited by even the most 

 highly differentiated animal tissues, were also to be found in 

 those of the plant. 1 



In my previous investigations I had shown that the tissues 

 even of ordinary plants gave electrical signs of excitatory 

 response. I now undertook an inquiry as to why they should 

 not also exhibit response by mechanical indications ; and I 

 was surprised to discover that ordinary plants, usually re- 

 garded as insensitive, gave motile responses, which had 

 hitherto passed unnoticed. 



From the point of view of its movements a plant may be 

 regarded in either of two ways : in the first place as a 

 mysterious entity, with regard to whose working no law can 

 be definitely predicated, or in the second place, simply as a 

 machine, transforming the energy supplied to it, in ways 

 more or less capable of mechanical explanation. Its move- 

 ments are apparently so diverse that the former of these 

 hypotheses might well seem to be the only alternative. 

 Light, for example, induces sometimes positive curvature, 

 sometimes negative. Gravitation, again, induces one move- 

 ment in the root, and the opposite in the shoot. From these 

 and other reactions it would appear as if the organism had 

 been endowed with various specific sensibilities for its own 

 advantage, and that a consistent mechanical explanation 

 of its movements was therefore out of the question. In spite 

 of this, however, I have attempted to show that the plant 

 may nevertheless be regarded as a machine, and that its 

 movements in response to external stimuli, though apparently 



1 Paper read before Royal Society, February 4, 1904. 



