126 CHAP. XII. MECHANISM OF PHOTOTROPIC CURVATURE 



growth : the effect is negative, i.e. retardation of growth, 

 when the stimulus is appHed at the responding region 

 of growth ; under intermediate conditions, the growth- 

 variation is diphasic, positive acceleration followed by 

 negative retardation. 



Fig. 68. Effect of indirect unilateral stimulation. 



s, s', induced negative tropic effect (movement avrayfrom 

 stimulated side) ; stronger stimulus s" gave rise to 

 negative followed by positive. (Crinum.) 



Experiment 74. Effects of indirect and direct electric 

 stimulation.— In the place of radio-thermal, I next appHed 

 electric stimulation. Taking a growing bud of Crinum 

 I determined the region of its active growth ; lower down 

 a region was found where the growth had practically dis- 

 appeared and could therefore be regarded as an indifferent 

 region. In order to observe the effect of indirect stimulation 

 on the rate of growth, I applied two electrodes on this 



