QUANTITY OF LIGHT AND PHOTOTROPIC CURVATURE 343 



The specimen employed was the terminal leaflet of Des- 

 modium gyrnns ; lij>ht was applied for a minute in the 

 two successive experiments for the two angles of 45*^ and 

 90°. The record (Fig. 127) shows that the phototropic 



Fig. 127. Fig. 128. 



Fig. 127. — EflEect. of angle of inclination of light on the tropic curvature of pulvinus. 

 The first response is to light at 45^ and the second, to 90^. (Betmodium gyrans). 



Fig. 128. — Series of tropic curvatures of growing bud of Crinnm to alternate 

 stimulation by light at 4.5^ and 90^. 



effect increases with the directive angle. In the present 

 case the ratio of the two effects is 1*6 : 1, which is not very 



different from the ratio 7^7^=1'4 



sin 45° 



I'vopic response of growing organs : Experiment 132. — 

 Similar experiment was carried out with the flower bud 

 of Crimini, held vertical. Light was applied alternately 

 at 45° and 90°, in two successive series. The object of 

 this was to make due allowance of possible variation of 

 excitability of the organ during the course of the experi- 

 ment. I have explained (p. 147), how the excitability of 

 a tissue in a condition slightly below par, is increased by 

 the action of previous stimulation. Series of responses 

 obtained under alternate stimulations at 45° and 90^ 



27 



