THE BACKGROUND CO2 FIXATION 



207 



certain steady level. The final r-valiie established in O2 atmosphere 

 was always higher than the steady r-level obtained in the N2 at- 

 mosphere. In the particular experiment illustrated by Fig. 1 the level 

 obtained in Oj was exceptionally low since the value was generally 

 from 2 to 10 times higher than the r level in N2 (c/. Fig. 4). This 

 factor depended upon the prehistory of the algae. 



EFFECT OF LIGHT 



The effect of light upon the D level was investigated with the 

 results shown in Fig. 2. The cells were first kept in the dark (flushed 



20 40 SO 



TIME IN MINUTES 



Fig. 2. Effects of transition from dark to light and from light to dark upon the 

 background C"02-fixing capacity. Measurement of background Ci*02-fixing 

 capacity {n) was made by subtracting R (i.e., the radioactivity fixed in 30-second 

 contact with Ci^02 in the dark) from R + r;, (i.e., the radioactivity fixed in 5 min- 

 utes under the same condition). The insets show, on a magnified scale, the events 

 occurring at earlier stages of illumination. 



with N2) for 50 minutes to make them adapt to the darkness and to 

 anaerobic conditions. Immediately after the Hght was turned on, the 



