THE ENERGETICS OF PHOTOSYNTHESIS 



105 



culture medium. The maintenance of a suitable CO2 pressure is of the highest 

 importance. In addition to these conditions, Warburg's arrangements for 

 the measurement of intensities and their absorption by the cells have to be 

 carefully observed. It does not matter whether the quantum requirement is 

 determined in acid medium with the two-vessel method or in alkaline medium 

 with the one-vessel method (see also compensation method on page 186). 



The discovery of the one-quantum reaction of photosynthesis showed that 

 every possible value for the quantum requirement could be obtained depend- 

 ing on the experimental conditions, as induced respiration depends upon these 



;jk^ ■ '^ 0/ 



90% 



Fig. 43. Comparison of photosynthedc efficiencies in the field and in tlie laboratory (Burk, 



Fed. Proc). 



conditions. This means that, after all, the magnitude of the quantum require- 

 ment of the over-all reaction is not so important as was believed. Of primary 

 importance is the fact that under optimal conditions it is 3. If higher values 

 are found, it may be concluded that experimental conditions are not optimal. 

 Since more attention has been paid to exact measurement with the large area 

 bolometer, Daniels (71) found, in 1955, quantum requirements of 8.9 in green 

 and 6 in blue, whereas he obtained a value of 157 in 1938 (33). Calvin (4) 

 succeeded in obtaining a value of 4.9 in red in 1955. In accordance with 

 errors shown by Warburg (41), these values should be reduced by 25 to 50%. 



