XXXV.— EFFECT OF TEMPERATURE ON PHOTOTROPIO 



CURVATURE 



By 



Sir J. C. BosE, 



Assisted by 



GURUPRASANNA DaS. 



I SHALL in this chapter deal with certain anomalies in 

 phototropic curvature, brought about by variation of tem- 

 perature and by seasonal change ; cerlain organs again 

 are apparently erratic in their phototropic response. 



SEASONAL CHANGE OP PHOTOTROPIC ACTION. 



Sachs observed a positive phototropic curvature in the 

 stems of l^ropceolum majus in autumn ; but this was 

 reversed into negative in summer ; similarly in the 

 hypocotyl of Ivy, the positive curvature in autumn is 

 converted into negative curvature in summer. 



Certain organs are apparently insensitive to the action 

 of light. Thus no phototropic response is found in the 

 tendril of Passijiora even under the action of strong 

 light. The tendrils of Vitia and Ampelojsis exhibit, 

 according to Wiesner, positive phototropism under feeble, 

 and negative phototropism under strong light. 



The anomalies referred to above may be explained by 

 taking into consideration the modifying influence of 



