PREFACE 



I have in this work dealing with my researches on the 

 irritability of plants introduced new methods by which 

 the scope of investigation has been enlarged, and a very 

 high degree of accuracy secured. In my previous treatise 

 on Plant Response, the response recorder employed was a 

 modification of the optical lever, automatic records being 

 secured by the very inconvenient and tedious process of 

 photography. The delay thus imposed retarded seriously 

 the progress of the research. Those practically engaged in 

 investigations on plants can realise the difficulties that 

 arise from the too quick passage of the seasons. It thus 

 frequently happened that by the time new instrumental 

 appliances were rendered practicable the favourable season 

 for the plant was over, involving the postponement of the 

 experiment for another year. In spite of these difficulties, 

 the long series of investigations that I then carried out gave 

 many interesting results, which not only threw light on 

 many obscure problems, but also led to the discovery of 

 several important phenomena in plant physiology. 



Some of these results, moreover, tended to cast doubt 

 on certain conclusions that had found universal acceptance. 

 It has, for example, been held that there was no trans- 

 mission of true excitation in Mimosa, the propagated 

 impulse being regarded as merely hydro-mechanical. The 

 question whether the transmitted impulse was physical or 

 physiological could only be satisfactorily decided if the 

 plant could itself be made to record the velocity of its 

 impulse and the changes induced in that velocity under 

 physiological variations. This is but one out of several 



