34 RESEARCHES ON IRRITABILITY OF PLANTS 



mode of excitation. In subsequent chapters we shall also 

 stud}^ in detail the various characteristics of response and 

 its time-relations. 



Summary 



The ideal method of stimulating a plant is one in which 

 the intensity might be maintained uniform or varied in a 

 definite and known manner. 



If the stimulus exceeds a certain critical value, the 

 tissue is injured with concomitant diminution or abolition 

 of excitability. 



One practical method of quantitative stimulation is 

 by electro-thermic stimulus, where the plant-tissue is sub- 

 jected to a sudden and definite thermal variation. 



The plant may also be excited by the action of a constant 

 current. 



Another method of excitation is by the discharge of a 

 condenser. 



And lastly, excitation may be induced in the plant by a 

 single induction-shock or by a series. As in the skeletal 

 muscle of animals, so in the pulvinus of Mimosa, the break- 

 shock is more effective than the make-shock. 



