346 O. WARBURG et al., S. B. HENDRICKS VOL. 4 (1950) 



The volume of our vessel was 37.0 ml and the volume of the liquid phase 16.53 rnl- For 10° C 



Therefore 



— 1.3 2.78 3.40 



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

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

 rements of 4 against 10 to 12. 



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

 quantum-efficiency measurements in carbonate-bicarbonate solutions at pfj 9.1, which kept the COg- 

 pressure constant instead of using culture medium at pn 4-9- They claimed^ 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 pn 5- The quantum values observed in the following time sequence 

 were 



I 



In carbonate mixture at pn 9 



In culture medium at pn 5 



In carbonate mixture at pn 9 



In culture medium at pn 5 



In carbonate mixture at pn 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 



^ O. Warburg, tjber die katalische Wirkung der lebendigen Substanz, Julius Springer, Berlin 1928. 

 ^ J. Franck and W. E. loomis, Photosynthesis in Plants, The Iowa State College Press, Ames, 



Iowa 1949. 

 ^ O. Warburg and V. Schocken, Arch. Biochem., 21 (1949) 363. 

 * O. Warburg, Am. J . Botany, 35 (1948) 194. 

 ^ R. Emerson and C. M. Lewis, Am. J. Botany, 28 (1941) 789. 



Received June nth, 1949 



