SUMMARY 197 



between the energy of radiation in different parts of the 

 spectrum and the corresponding activity of photosynthesis. 



Photosynthesis is feebly initiated even under infra-red 

 radiation. In the visible spectrum the activity at first 

 increases gradually ; at B the maximum of activity is 

 reached, though the intensity of radiation is here lower ; 

 beyond B, the activity undergoes a decline parallel to the 

 fall in the intensity of radiation of the successive rays. 



The maximum of activity at B is due to absorption of 

 these particular rays by the chlorophyll as shown by its 

 spectrum. There is, however, no second maximum at the 

 second absorption-band in the blue-violet between F and G. 



Experiments are described which tend to prove that 

 these blue-violet rays are concerned in inducing photo- 

 tropic curvature. Hence the A and the D effects of light 

 are complementary to each other. The rays which are 

 most effective for photosynthesis are ineffective for tropic 

 stimulation and vice versa. 



The effects characteristic of the different regions of the 

 spectrum are due (1) to the energy of the rays ; (2) to the 

 degree of their absorption ; and (3) to the complementary 

 A and D reactions in induction of photosynthesis and of 

 phototropism. 



