REACTION PATTERNS IN PHOTOSYNTHESIS 



79 



By varying the duration of the flashes, we obtauied the different 

 shapes of absorption changes with respect to time, as shown in Fig. 5. 

 In these experiments we always used saturating intensities. Passing 

 from short to longer flashes there is an increase in the change of ab- 

 sorption. At a critical flash time this increase in the change of ab- 

 sorption stops, and a second strong but slow increase of absorption 

 follows. This shows the existence of two phases of the change of 

 absorption: a first fast one and a second slow one.* 



tim e (- 



/ sec 



Fig. 5. Change of absorption of Chlorella at 515 m/x as function of time by 

 lighting the Chlorella with flashes of Hght of different durations (see figures about 

 the picture), id ~ 1 second. 



The first fast phase of the absorption changes is as independent of 

 temperature as the effect of short flashes (Fig. 6). By contrast the 

 second phase decreases with decreasing temperature until at 5°C. 

 there is almost no second phase. In the dark after long flashes the 

 decline is again a function of temperature, as we have seen after short 

 flashes. 



The second slow phase depends also on the dark time between the 

 flashes. 



A second phase can be observed also in the decrease in absor{)tion 

 at 475 mn. The change of this phase by different temperatures and 

 dark times is very similar to the change of the second phase at 515 

 m^t. This means that the change of absorption at 515 m^u and 475 

 mix probably belongs to one and the same reaction. 



On the basis of these experiments we postulate three reactions 

 during the primary process. 



* Duysens has reported changes of absorption in steady light at 515 mn and 

 478 mfx (4). Probably these changes correspond to the end point of the second 

 alow phase. 



