EFFICIENCY OF PHOTOSYNTHESIS 



351 



woiikl ])(>. uncertain, because current methods of measuring? the frac- 

 tion of incident Hght absorbed by thin suspensions are not suffi- 

 ciently precise. Methods of measuring scattered Hght are imperfect, 

 and errors vary with distribution of scattered Ught, which in turn 

 varies from one sample of cells to another. However, the question 

 whether in thin suspensions the (]uantum requirement of photos^ni- 

 thesis is different above and below the compensation point may be 



_ 8 



Q. 



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 a. 



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o 

 o 

 Q. 



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2 4 6 8 .2 



Incident Energy— ^ einsteins per min, over 10 sq.cm. 



Fig. 1. Rate of photosynthesis as a function of hght intensity, showing Unearity 

 through the region of compensation of respiration. The right-hand figure shows the 

 lowest portion of the left-hand figure, plotted on an expanded scale so that ail ob- 

 servations can be shown. 



investigated simply by measuring the rate of photosynthesis as a 

 function of intensity of incident light. We ha\'e made a number of such 

 measurements with samples of cells grown and prepared in different 

 ways. In all cases we have found that, within the limits of error of 

 our experiments, the rate of photosynthesis is a linear function of light 

 intensity from zero through the region of compensation of respira- 

 tion and up to intensities several times compensation. We have never 

 observed a change in .slope at or near the compensation point. 



