FATIGUE-RELAXATION I35 



Fatigue-Relaxation 



There is a difficulty in connection with the reversal of 

 positive curvature into negative which cannot be explained 

 simply by the conduction of excitation transversely from the 

 stimulated to the opposite side ; for, in a radial organ, the 

 contraction of the distal side cannot be greater than that of 

 the directly excited proximal side. There must therefore 

 be an additional factor in operation, which has to be 

 discovered. 



The following experiments prove that it is fatigue-relaxa- 

 tion which occurs in a tissue under continued stimulation. 



As an example, in illustration of this fact, may be cited 

 the erectile movement of the leaf of Mimosa after continuous 

 stimulation. When the leaf is subjected to brief electric 

 stimulation there is an immediate fall of the leaf, due to 

 active contraction of the more effective lower half of the 

 pulvinus. The leaf then exhibits normal erectile recovery. 

 When the leaf is subjected to continuous stimulation it 

 also exhibits a preliminary fall with subsequent erection 

 of the leaf, this erection being due to fatigue-relaxation 

 of the lower half of the organ. ^ The result is not unHke 

 the contraction of a muscle passing into relaxation under 

 continuous stimulation. 



The preliminary phases culminating in fatigue-relaxation 

 in growing organs I propose to demonstrate : 



1. Under different intensities of stimulation, successively 



applied to the plant ; and 



2. Under uniform strong intensity, but increasing 



duration of application. 



I will first describe the general effects of brief and of pro- 

 longed electric stimulation on growing organs. 



Experiment 80. Normal contraction and recovery after 

 brief electric stimulation. — I took a specimen of Cow-pea 

 {Vigna Catjang) and obtained record of its normal rate of 



1 The Motor Mechanism of Plants (1928), p. 



