80 



H. T. WITT 



1. The first rise of absorption is probably due to a photochemical 

 reaction F. In this reaction unknown molecules X (absorption band 

 '^475 niyu) are transformed to Y (absorption band '^blb m^u). 



2. Durbig the temperature-dependent, slow second rise of absorp- 

 tion a rate determining chemical reaction C must be involved. This 

 reaction releases further molecules X, which are also transformed by 

 light to Y. 



2a'c 



15° C 



ire 



5'C 



5 W'" sec 



time 

 Fig. 6. Change of absorption of Chlorella at 515 m/x as function of time at tem- 

 peratures between 24°C. and 5°C. U = 0.52 second, ta = 0.93 second. 



3. The temperature-dependent decline in the dark time after the 

 flash is connected with a chemical dark reaction D. In this reaction the 

 molecules Y built up in the light, are reacting with one or more 

 unknown molecules Z to form X and Z'. 



After the discovery of chlorophyll fluorescence in plants (7) the 

 change of fluorescence was used for investigations of photosynthesis. 

 Unfortunately there exists no definite correlation between the change 

 of fluorescence and the occurrence of other reactions on chlorophyll 

 for large molecules. This fact makes it difficult to interpret the meas- 



