PHOTOTROPISM 317 



of the bean plant. The source of illumination was 82 c.p, 

 electric lamp, enclosed in a metallic tube with circular 



Fk;. 112. — Successive positive responses of the terminal leaflet of bean. Light 

 applied from above for 20 seconds ; complete recovery in 3 minutes. 



aperture for passage of light. The leaflet was attached to 

 an Oscillating Recorder. Light was applied on the upper 

 half of the pulvinus for 20 seconds ; this induced an up- 

 movement of the leaflet, due to the contraction of the 

 upper half of the organ. Recovery took place in course 

 of 8 minutes (Fig. 112). 



POSITIVE PHOTOTROPIC CURVATURE OP GROWING 

 ORGANS. 



Effect of moderate stimulation : Experiment 118. — I shall 

 presently show that the intensity of phototropic reaction 



