76 



H. T. WITT 



We were searching for changes of absorption between 400 mn and 580 



When photosynthesis is started by flashes of Hght, there is a rapid 

 increase of a new absorption band at ^^515 m/x. At the same time 

 (within the accuracy of measurement) a decrease of absorption takes 



,o 



I- 



o 



01 



4j 







1 ■ 







10 W^ sec 



time 



Fig. 1. Change of absorption of C/iZoreZto as function of time. At time < = the 

 Chlorella were lighted by a flash of light, ti = 5 X 10"^ second, td = 0.5 second. 

 Temperature 19 °C. Upper cuive: change of absorption at 515 m/*. The change 

 from to 1 corresponds to an increase of absorption. Lower curve: change of 

 absorption at 475 myu- The change from to 1 corresponds to a decrease of absorp- 

 tion. 



place with a maximum at about 475 m/x (3) (Fig. 1).* The relative 

 change of absorption is only of the order of a tenth of a per cent. Using 

 flashes as short as 3 X 10~^ second we observe a change of absorption 

 within the duration of the flash. This change must, therefore, take 

 place within the time of 3 X 10 ~^ second or less. In the dark time 

 after the flash, the change of absorption disappears completely within 

 '-^lO"^ second. 



With an increase of light intensity there is also an increase of the 

 change of absorption (Fig. 2) . At high intensities there is a saturation 

 of the absorption changes. The intensity at the saturation point is of 

 the order of that which suffices to saturate photosynthesis. 



* In text of all figures t[ means: duration of hght flash, ta: dark time be- 

 tween the flashes. 



