128 CHAP. XII. MECHANISM OF PHOTOTROPIC CURVATURE 



with a different experiment which shows, in an identical 

 specimen, (i) an acceleration of growth under indirect and 

 (2) a retardation of growth under direct stimulation. 



Experiment 75. Effect of long-continued indirect stimu- 

 Jation. — In the case of Mimosa, it was shown that indirect 



Fig. 70. Effect of continuous indirect electric stimulation E. 



Preliminary enhancement of growth followed by excitatory con- 

 traction. Interval ofsuccessive dots 10 seconds. (Cosmos.) 



stimulation induced at first a positive response, w^hich was 

 transformed into negative under prolonged action. Parallel 

 results were obtained with Cosmos under continuous electric 

 stimulation ; there was a preliminary enhancement of growth 

 shov/n by the up-curve, followed by excitatory contraction 

 (down-curve) due to the conduction of true excitation (fig. 70). 



Electric Response to Direct and Indirect 



Stimulation 



Employing the electric method of investigation, I have 

 obtained with different organs the positive, the diphasic, and 

 the negative electric responses corresponding to the mechani- 

 cal responses given by both motile and growing organs. 



Experiment 76. Electric Response. — I took a leaf of Bryo- 

 phyllum calycinum, and made suitable electric connections. 



