124 



PHOTOSYNTHESIS 



had developed for the effect of nutrients on crop yield, to the effect of 

 carbon dioxide on the rate of photosynthesis. He found, however, that 

 the calculated values are not in accord with the experimental results. 



In the second set of Harder "s experiments he endeavored to determine 

 the effect on the rate of photosynthesis of altering two factors. He argues 

 that according to Blackman's view, only that factor which is limiting 

 should affect the photosynthetic rate. The experimental results do not 



2,000 



6.000 



10,000 



14,000 



18,000 M.C. 



Fig. 10. — Effect of change in light intensity on the rate of photosynthesis of 

 Fontinalis with different concentrations of carbon dioxide. (From Harder.) 



support this conclusion. A series of experiments with six different light 

 intensities and four concentrations of potassium bicarbonate showed that 

 an increase in either light intensity or carbon dioxide-concentration re- 

 sulted in an augmented photosynthetic rate. The latter is therefore de- 

 pendent upon both these factors under all circumstances. Harder's results 

 are reproduced in Figures 10 and 11, 



From these curves it appears that with either factor held constant 

 an increase in the other factor results in a rise in the rate of photosyn- 

 thesis. The effect of the factor which is varied is not the same through- 

 out the course of the curve but depends upon the intensity of the other 



