W. J. V. OSTERHOUT AND A. R. C. HAAS • 9 



The suggestion which first ofifers itself is that photosynthesis be- 

 longs to the class of autocatalytic processes, in which the reaction is 

 catalyzed by one of its own products. Such reactions begin slowly 

 but as more of the catalyzing substance is produced the reaction goes 

 on at an increasingly rapid rate until it begins to slow down as the 

 reacting substances are used up. If these substances are constantly 

 renewed, the reaction will not slow down but continue to go on more 

 and more rapidly. 



PHOTOSYNTHESIS 



7 5 MINUTES 



Fig. 1. Curve showing that where Ulva is exposed to light the speed of photo- 

 synthesis increases until a steady rate is attained. The dotted line expresses a 

 uniform rate. 



In our experiments on photosynthesis the reacting substances are 

 constantly renewed.'^ The substances entering into the reaction are 

 presumably carbon dioxide and water. The concentration of the 

 water remains constant, while as soon as the concentration of the car- 

 bon dioxide has diminished by a very small amount it is brought back 

 to the original point by the renewal of the sea water. 



^^ When the sea water is not changed during the experiment the curve rises 

 more rapidly at first, then bends over to the right as the supply of CO2 is used up. 



