48 CHAP. VI. RELATION BETWEEN LIGHT AND PHOTOSYNTHESIS 



Taking all the factors into account, we find that the 

 activity of photosynthesis is proportional to the quantity of 

 incident light. 



Summary 



The limiting maximum in photosynthesis is found to be 

 relative and not absolute. It increases with the intensity 

 of light, this increase being independent of the C0 2 -con- 

 centration of the liquid in which the plant is immersed. 



The Hydrilla plant is very sensitive to differences in the 

 intensity of light, and may therefore be employed as a 

 photometer. 



A definite physiological equivalence was found between 

 sunlight and Pointolite. On a bright day in March, sun- 

 light 0-04 S was found to be physiologically equivalent to 

 1700 lux Pointolite ; that the two lights were also physically 

 equal was subsequently demonstrated by a grease-spot 

 photometer. 



Photosynthesis is shown to be proportional (1) to the 

 duration, (2) to the intensity, and (3) to the sine of the 

 directive angle. The amount of photosynthesis is therefore 

 proportional to the quantity of incident light. 



