QUANTUM YIELD 1947 



Adding nutrient salts (MgS04, Ca(N03)2) to the carbonate medium 

 was found to improve the yield. 



The decline of the yield with time, observed in bicarbonate-washed cells, 

 was taken as evidence that factors other than the momentary CO2 concen- 

 tration can affect the rate in alkahne media. Therefore, the yields ob- 

 served in a carbonate ])uffer with a certain [CO2] value sometimes may not 

 fall on the curve of fig. 37D.27; in particular, one might conceivably find 

 the same (low) yield at all CO2 concentrations. (This remark by Warburg 

 ei al. forestalls criticism which could be based on Emerson's and Whitting- 

 ham's findings of the independence of quantum yield from carbon dioxide 

 concentration.) Warburg et al. suggested that, whenever the yield in 

 carbonate buffer is below the values predicted by fig. 37D.27, this is "a sure 

 sign of progressive changes in the cells, probably, a diffusion of bicarbonate 

 into them." Gaffron's experiments (c/. section 1) agree with these conclu- 

 sions in that they, too, indicate that ChloreUa cells may or may not respond 

 to changes in [CO2] between 0.2 and 5%, depending on the conditions of 

 their culturing. However, Gaffron's measurements indicated (for strong 

 light) an early decline of the rate with decreasing [CO2] in cells conditioned 

 to high CO2 concentrations, rather than — as suggested by Warburg's obser- 

 vations — a continued increase of the rate, in these algae, with increasing 

 [CO2], beyond the saturation rate of the "bicarbonate algae." 



The above-described results of Warburg and co-workers contradicted 

 not only the quantum yield measurements of other observers (despite the 

 assertion, made in 1950, that the quantum yield measurements have be- 

 come so simple as to be suitable for student's experiments!), but much of 

 the general experience in the field of photosynthesis — such as observations 

 on the dependence of the yield on [CO2] (chapter 27, and this chapter, 

 sections 1 and 2) and wave length (chapter 30); the radiocarbon data 

 (chapter 36) ; and the induction and intermittency studies (chapters 33, 34) . 

 Furthermore, the successive results, presented by Warburg and co-workers 

 in the 1924, 1948, 1950 and 1951 papers, contradicted each other in many 

 respects (e. g., in the pretreatment recommended to obtain cells of highest 

 efficiency, and the best conditions — fight intensity, pH, intermittency, 

 etc. — needed to demonstrate this efl&ciency). 



If one nevertheless accepts all the reported observations as experimen- 

 tally correct, one is led to the conclusion that, for each pretreatment, dif- 

 ferent conditions and a special schedule of measurements must be worked 

 out to calculate the highest yields. These facts made Franck suggest in 

 1953 that Warburg, Burk et al. were measuring, in 1950-52, not normal, 

 steady photosynthesis, but certain transient phenomena, which can be 

 strongly enhanced by various treatments — including starvation, prolonged 

 shaking, high carbon dioxide concentration, etc. These transient phenom- 



