28 PLANT RESPONSE 



due to hydrostatic disturbance. The true excitatory response 

 takes place later. 



Besides the isotonic response, obtained by recording the 

 actual movements of the excited leaf, it is also possible 

 to record the isometric response where the movement is 

 restrained, and the variation of tension caused by the con- 

 traction of tissue is alone recorded. 



The intensity of a minimally effective stimulus in the 

 case of Biopliytum is definite. This value undergoes appro- 

 priate variation with the variation of excitability of the 

 organ. 



