122 



PLANT RESPONSE 



response of plants (fig. 64). It need only be mentioned, 

 further, that exactly the same preliminary staircase effect, 

 reaching a maximum, and followed by fatigue, is found in 

 the responses of muscle (fig. 65). 



The inference that the occurrence of the staircase effect 

 is due to the gradual removal of molecular sluggishness, 

 receives further support from the following experiment on 

 a plant where sluggishness is brought on artificially, and 



made to disappear gradually. 

 Sluggishness may be induced 

 in a tissue by cooling, this con- 

 dition being made to disappear, 

 by the gradual return of the 

 substance to the ordinary tem- 

 perature of the room. On carry- 

 ing out such an experiment, 





Fig, 65. Preliminary Staircase, 

 followed by Fatigue, in the 

 Responses of Muscle (Brodie) 



Fig. 66. Staircase Increase 

 in Electrical Response of 

 Petiole of Bryophyllum, 

 rendered sluggish by 

 cooling 



and recording the successive electrical responses to successive 

 uniform stimuli, I obtained, as I had expected, a marked 

 staircase effect (fig. 66). 



Merging of physical into chemical phenomena.— 

 I have explained that responsive phenomena are primarily 

 due to the molecular distortion caused by stimulus, that is to 

 say, they are of a physical character. Fatigue has also been 

 shown to be primarily due to residual strain. But it must be 

 borne in mind that in the borderland between physics and 

 chemistry there is no sharp line of demarcation. For ex- 

 ample, yellow phosphorus under the stimulus of light is 



