30 RESEARCHES ON IRRITABILITY OF PLANTS 



excitable, and excitation was caused by the discharge of 

 •I microfarad condenser charged to -3 volt. 



Stimulation by Induction-shock 



Excitation may be induced by means of a single or 

 repeated shock from an induction coil. In my own expe- 

 rience I was at first under the impression that this mode of 

 stimulation was not suitable for repeated quantitative 

 experiments, as I found that the plant was liable to become 

 insensitive owing to the fatigue or injury caused by the shock. 

 Later, however, I was able to trace this difficulty to the 



Fig. 10, — Record of responses to stimulation by 

 condenser discharge. 



employment of an intensity of shock which was in excess 

 of a certain critical value. I had in fact been misled by 

 the prevaiHng belief that the excitabiHty of the plant 

 was considerably lower than that of the animal. Hence 

 I employed an intensity of current which was unnecessarily 

 high. This induced fatigue and consequent insensitiveness. 

 Afterwards I discovered that in so far as its sensitiveness 

 to electrical stimulation was concerned, Mimosa was in no 

 way inferior to the animal. Quantitative results will be 

 given later, in justification of this statement. Avoiding, 

 then, an intensity of stimulus which was too great, and 

 allowing proper resting-intervals, I found that the efficiency 

 of induction-shock as a mode of stimulation was all that 

 could be desired. It has also the great advantage of 



