II. T. WITT 



These experiments make it probable that the changes of absorption 

 are a direct reflection of partial processes in photosynthesis. That the 

 last change is one of the first steps in the primary process can also be 

 f-hown in the following way. 



c 

 o 



o 



CO 



-Q 

 OJ 



o 



b,5°L 



W.5'C 



15°C 



29 'C 



tOW^ sec 



time 

 Fig. 4. Change of absorption of Chlorella at 515 m^ as function of time at 

 temperatures between 5.5 °C. and 29 °C. At the time t = the Chlorella were 

 lighted by a flash of light, ti = 4 X 10 ~' second, td = 0.76 second. The arrows are 

 indicating the half-time of the lifetime. 



It is known that HON (6) and quinone act as inhibitors by block- 

 ing the cycle of carbon dioxide. But the change of absorption takes 

 place even in the presence of these poisons. Furthermore one can see 

 the change of absorption of chloroplasts outside the living cell (3). 

 On the other hand, urethane is a strong poison for the primary process. 

 Correspondingly we found with increasing urethane concentration a 

 decrease in the change of absorption. This inhibition is reversible; 

 after washing you can restore the original change. 



To obtain more accurate information about the mechanism of this 

 process we measured the change of absorption as a function of several 

 parameters. 



