TRANSIENTS FOR CARBON DIOXIDE 



433 



The next observation I wish to discuss is seen in Fig. 3. The two 

 heavy Hnes are 160 seconds apart. The hght is turned on at the heavy 

 line on the left, and off at the one on the right. The lower curv^e tells us 

 how in a matter of a second or two the direction of the metabolic gas 

 exchange may change upon illumination. The upper curve contains the 

 feature that I find interesting. Here the first effect of light is to com- 

 pensate respiration only. This com'pcnsation period lasts 20 to 40 sec- 



6.9 



- 7.0 





72 



Fig. 3. Recording of induction periods in Chlorella under different conditions 

 after repeated short dark and light periods. Length of light period between the two 

 vertical lines: 160 seconds. Upper curve: 0.7% cell volume in 0.002 M bicarbonate 

 between pH 6.4 and 6.9. Two-day culture in Warburg medium. Lower curve: 

 0.9 cell volume in 0.004 M bicarbonate between pH 7.5 and 7.9. Four-day culture 

 in 0.05 M bicarbonate medium. 



onds — in other cases even longer — and only after that time does photo- 

 synthesis start in earnest. This compensation effect is not a rare oc- 

 currence and not restricted to Chlorella. It was found also with 

 Scetiedesmus and Stichococcns. In acid media it seems to be the rule. 

 It can be made to disappear when the algae have been grown in bi- 

 carbonate instead of in acid phosphate buffer, as was the case with 

 the Chlorella producing the lower curve in Fig. 3. It may not be 

 superfluous to emphasize that these observations have been made 

 innumerable times during the past four years. 



