104 



PHOTOSYNTHESIS 



course of the curve but depends upon the intensity of the other factors. 

 When the other factors, carbon dioxide-concentration, temperature, etc., 

 are relatively high and light intensity is low, the increase in the rate of 

 photosynthesis is about proportional to the increase in light intensity. As 

 the latter factor continues to be augmented the effect on the rate of photo- 

 synthesis becomes less, so that the curve flattens, and the influence of other 

 factors becomes noticeable. Such curves of the effect of light intensity 

 have been obtained by Boysen-Jensen,«^ Warburg '' and Harder '^ and are 

 reproduced in Figure 8. 



Fig. 8. — The influence of light intensity on the rate of photosynthesis of Chlorella. 

 The ordinate represents the rate of photosynthesis, the abscissa the illumination 

 intensity. (From Warburg.) 



Harder measured the photosynthetic activity of Fontinalis at different 

 light intensities and varying carbon dioxide-concentrations. The light 

 intensity of the highest was 216 times that of the lowest intensity, and 

 the carbon dioxide-concentration was varied from 0.01 to 0.32 per cent. 

 The results are shown in Table 19 and represent true photosynthetic rates. 



'^ Boysen-Jensen, P., Bot. Tidsskrift, 36, 220 (1918). 

 '"Warburg, O., Biochcm. Zcit., 100, 255 (1919). 

 "Harder, R., Jahrb. wiss. Bot., 60, 531 (1921). 



