io8 



PLANT RESPONSE 



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

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



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

 Response of Plants 

 {a) Stimulation by tetanising electric shocks ; {d) stimulation by rapidly 

 succeeding thermal shocks. Continuous lines represent action during 

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

 Passiflora, 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, b). 



I have already described 

 curious instances of alter- 

 nating fatigue exhibited in 

 successive single responses 

 to single stimuli (fig. 54). 

 A very curious and interest- 

 ing effect of this nature 

 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 



Fig. 58. Photographic Record of 

 Periodic Fatigue under Continuous 

 Stimulation in Contractile Response 

 (Filament of Uriclis Lily) 



