144 PHOTOSYNTHESIS 



evolution of Og. If now equation /5 holds with n = 2 then it 

 must be supposed that in the photoreduction by Scenedesmus 

 oxygen is replaced by another oxidant resulting from the 

 light reaction, and that the same situation may also apply to 

 photosynthesis. 



Several years ago G. E. Briggs pointed out that if some 

 chemosynthetic process was taking place in photosynthesis 

 the gas exchange would not be linear at the beginning of 

 either light or dark periods. There should, for example, be 

 an increase of Og production and a deficiency of COg uptake 

 at the beginning of a light interval; it being assumed that 

 the induction effects were sufficiently small. Quite recently 

 as mentioned in Chapter 4, Burk and Warburg (1951) have 

 some evidence for such an effect. Their experiments with 

 Chlorella were carried out with alternate light and dark (or 

 compensating) intervals of the order of i minute. It was 

 concluded that there was a greatly increased output of 

 oxygen in proportion to the absorbed light energy at the 

 beginning of the light interval. However, in contrast to the 

 possibility envisaged by Briggs, there was an equal increase 

 of uptake of COg. Then during the dark interval there was 

 initially a greatly increased Og uptake together with a 

 corresponding increase in CO2 production over and above 

 that of the dark respiration measured over a long period. 

 The net photosynthesis over the light and dark period taken 

 together was the same as that observed under continuous 

 illumination. 



The conclusions of Burk and Warburg are based on 

 minute changes in the level of the manometric fluid rapidly 

 read with vigorous shaking throughout the short alternate 

 intervals of illumination. It is difficult to see how the gas 

 liquid equilibrium could be established to allow results of 

 the accuracy claimed to be obtained during short intervals. 

 Against this criticism it must be emphasized that it is pos- 

 sible when using a well-tried method to make qualitative 

 deductions beyond those apparent from the formal statement 

 of the actual measurements: many discoveries have been 

 initiated in this way. Confirmation of these results by other 

 methods is awaited. 



