THE NATURE OF PHOTOSYNTHESIS 



125 



factor. Harder therefore concludes that a variation in the intensity of 

 that factor which is relatively to the greatest degree in minimum con- 

 centration or intensity produces the greatest change in the photosynthetic 

 rate. This is a rather awkward statement. It is Harder's conception 

 that the relation of the photosynthetic rate to the two factors, carbon 

 dioxide-<:oncentration and light intensity, is a complicated one and that 

 these two factors are mutually interdependent. The augmenting effect 



Fig. 11. — Effect of change in concentration of carbon dioxide on the rate of photo- 

 synthesis with different intensities of light. (From Harder.) 



of an increase of one of these factors is not the same at all concentra- 

 tions or conditions of intensity of the other factor. In fact, the augment- 

 ing effect of the first factor will be higher the greater the intensity of 

 the second factor. In other words, the higher the light intensity, the 

 greater will be the augmenting effect of an increase in carbon dioxide- 

 concentration and the higher the existing carbon dioxide-concentration, 

 the greater will be the rise in the photosynthetic rate caused by an in- 

 crease of the light intensity. 



From what has already been said it is evident that in any endeavor to 

 determine the effect of carbon dioxide-concentration on photosynthesis, 

 in any quantitative sense whatsoever, it is essential that the other factors 



