IOS PLANT RESPONSE 



reversal, the tissue is incapable of the normal excitatory con- 

 traction, but after a period of rest of about seven minutes it 



FlG. 57. Fatigue under long-continued Stimulation in the Contractile 

 Response of Plants 



(ci) Stimulation by tetanising electric shocks ; (b) stimulation by rapidly 

 succeeding thermal shocks. Continuous lines represent action during 

 stimulation ; dotted lines represent after-effect (coronal filament of 

 Passijfora, magnification forty times). 



again gives response, which is at first normal, and then, after 

 reaching a maximum, becomes reversed. The second re- 

 sponse is, however, seen to be smaller than the first. 



I obtained parallel results 

 under the action of rapidly 

 succeeding thermal shocks 

 (fig- 57, V). 



I have already described 

 curious instances of alter- 

 nating fatigue exhibited in 

 successive single responses 

 to single stimuli (fig. 54). 



FIG. 58. Photographic Record of A ver y curious and interest- 

 Periodic Fatigue under Continuous j n g effect of this nature 

 Stimulation in Contractile Response 



(Filament of Uridis Lily) occurring under continu- 



ous electric stimulation, is 

 shown in the accompanying photographic record (fig. 58) 

 of responses given by the filament of Uriclis Lily. It will 



