370 



LIGHT AND LIFE 



\i 



12.8 °C 



80 



LIGHT INTENSITY 

 klux 



100 



Fig. 6. Relative contribution of the ESR signals at g = 2.002 (open circles) and 

 at g — 2XWi (closed circles) to the total signal intensity of Chlorella cells at 

 various light intensities, at temperatures of 29.5°C and 12.8°C. See text for details 

 of measurement. 



11 seconds and 20 seconds respectively) during decay in the dark. 

 By methods which have been described elsewhere (5) , it is possible 

 to estimate the relative contribution ol the two processes to the total 

 ESR signal. Results of such an analysis of the ESR signal exhibited 

 by Chlorella at various temperatures are shown in Fig. 7. The upper 

 curve shows that at all temperatures the signal appears after onset 

 of light with a single, relatively long time constant. The signal in- 

 tensity is at a minimum at 18-28°C, and is maximal at low tempera- 

 tures. When illinnination stops, the decay process exhibits two time 

 constants. The fast component makes almost no contribution to the 

 decay process at temperatures of 18-28°C, but represents an increas- 



