PREFACE vii 



definite electro-motive changes, was regarded as highly 

 controversial. Indeed, in the discussion which followed 

 the reading of my Paper, on June 6, 1901, Sir John Burden 

 Sanderson went so far as to state that this excitatory 

 response of ordinary plants to mechanical stimulation was 

 an impossibility. 



My next investigation was directed towards the question 

 whether the responsive effects which I had shown to occur 

 in ordinary plants might not be further exhibited by means 

 of visible mechanical response, thus finally removing the dis- 

 tinction commonly assumed to exist between the ' sensitive ' 

 and supposed non-sensitive. These results were published 

 in my work on Plant Response, 1 where the effects of various 

 environmental stimuli on the different plant organs were 

 demonstrated by means of responsive movements. Many 

 anomalous effects hitherto ascribed to specific sensibilities 

 were here shown to be due to the differential excitability 

 of anisotropic structures, and to the opposite effects of 

 external and internal stimuli. Among other things, it was 

 there shown that internal stimulus was in reality derived from 

 external sources, and that the term ' autonomous response ' 

 was a misnomer, since all movements were due, either to the 

 immediate effects of external stimulus, or to stimulus previously 

 absorbed and held latent in the plant, to find subsequent ex- 

 pression. It was further shown that not gross mechanical 

 movements alone, but also other invisible movements, were 

 initiated by the action of stimulus ; that external stimulus, 

 so far from invariably causing a run-down of energy, more 

 often brought about its accumulation by the plant ; and that 

 the various activities, such as the ascent of sap and growth, 



1 Plant Response as a Means of Physiological Investigation, 1906. 



