The Quantum Efficiency of Photosynthesis 91 



where the underlined values are the values used and obtained in 1923. This calculation shows that 

 Emerson's objection was not very significant and could not explain the divergent quantum requi- 

 rements of 4 against 10 to 12. 



II. In an effort to avoid difficulties caused by fiuctuations of y. Emerson and Lewis made 

 quantum-efficiency measurements in carbonate-bicarbonate Solutions at pH 9.1, which kept the 

 COi-pressure constant instead of using culture medium at pH 4.9. They claimed J that in such 

 alkaline Solutions the quantum-efficiency was the same as in the acid culture medium: "then we 

 find the yields measured in acid phosphate culture medium are in good agreement with those 

 measured in carbonate mixture". 



But the experimental data were not presented to substantiate this important Statement. We can 

 confirm Emerson's finding that in the carbonate-bicarbonate mixtures the quantum-requirement is 

 10 to 12, but we cannot confirm that the same quantum efficiency is obtained in the acid culture 

 medium. Data presented in protocol 3 show that very different quantum-efficiencies are obtained if 

 we determine the quantum efficiency of aliquot portions of a cell Suspension in carbonate mixture at 

 pH 9.1 and in culture medium at pH 5. The quantum values observed in the following time se- 

 quence were 



<P 

 In carbonate mixture at pH 9 10.5* 



In culture medium at pH 5 3.9* 



In carbonate mixture at pH 9 



In culture medium at pH 5 



In carbonate mixture at pH 9 



where the asterisked values were obtained above the compensation point and the others below the 

 compensation point. 



Maximum yields should therefore not be determined in the carbonate mixture, as has been done 

 frequently during the last 10 years. 



References 



1 Warburg, O., Über die katalischen Wirkungen der le- 3 Warburg, O., and Schocken, V., Arch. Biochem. 21 

 bendigen Substanz, Julius Springer, Berlin 1928. (1949), 363. 



2 Franck, J., and Loomis, W. E., Photosynthesis in 4 Warburg, O., Am. J. Botany 35 (1948), 194. 



Plants, The Iowa State College Press, Arnes, Iowa 5 Emerson, R., and Lewis, C. M., Am. J. Botany 28 

 1949. (1941), 789. 



