NONMANOMETRIC MEASUREMENTS OF QUANTUM YIELD 



1121 



graph to respond almost immediately to transitions from respiration (in 

 darkness) to photosynthesis (in light) and vice versa. In the top and 

 bottom curves, the illumination is below the compensation point, and 

 photosynthesis manifests itself in a reduced rate of consumption of oxy- 

 gen; in four other curves, the oxygen concentration increases during 

 photosynthesis. The curvatures of the respiration curves show the un- 

 certainty involved in calculation of the respiration correction. The rate 

 of oxygen consumption in the five minutes immediately following the cessa- 

 tion of illumination was used by the authors in the calculation of this cor- 

 rection. (This method gives the highest respiration correction and conse- 

 quently the highest quantum yield values.) 



in 



c 



T3 

 O 



41.00 - 



39.00 



•£ 37.00 



£ 

 o 



c 

 o 



> 



o 



z 



O 



35.00 



33.00 - 



t 31.00- 





o 



o 



>■ 



X 



o 



29.00 - 



27.00 - 



25.00 - 



20 



40 50 30 

 TiME.min 



100 



Fig. 29.6. Photosynthesis and respiration of Chlorella measured by a 

 polarograph (after Petering, Duggar and Daniels 1939). 



The experiments were made with white light; from 27 to 48% of the 

 incident light was absorbed by the suspension. The calculated quantum 

 yields ranged from 0.045 to 0.100, clustering around 0.07, and showing no 

 trend with light intensity in the range from 1000 to 6000 erg/cm. ^ sec. 



New experiments with the polarograph were conducted by Moore and 

 Duggar (1949). In these Chlorella cells were first illuminated with light 

 of one color (intensity, 800-2500 erg/cm. ^ sec.) and then light of another 

 color was added, and the additional yield determined. The idea behind 

 this procediu'e was that the uncertainty concerning the amount of respira- 



