16 DYNAMICS OF PHOTOSYNTHESIS 



and observing changes in the color of the indicator. In the case of 

 fresh water aquatics bicarbonates are added. 



By this method it is found that Ulva which has been kept in the 

 dark begins photosynthesis as soon as it is exposed to sunhght and that 

 the rate steadily increases until a constant speed is attained. 



This may be explained by assuming that sunlight decomposes a 

 substance whose products either catalyze photosynthesis or enter 

 directly into the reaction. 



Quantitative theories are developed in order to account for the 

 facts. 



