Il6 CHAP. XV. CO a -SUPPLY AND PHOTOSYNTHESIS 



unreliability of this method must account for his high value 

 of 20 mg. per ioo c.c. for the turning-point. Blackman's 

 results are in agreement with mine ; for he (by the method 

 of estimation of C0 2 absorbed) finds the maximum to be at 

 or about 10 mg. of C0 2 per ioo c.c. of water. 



Table XIVa. — Showing Photosynthetic Activity at Different 

 Concentrations of C0 2 (Pointolite) 



( Winter-specimens) 



I reproduce Blackman's average curve, which was ob- 

 tained from irregularly distributed points. The causes of 

 these irregularities are explained by Blackman as follows : 



' With Elodea the assimilation values along the horizontal 

 part of the curve are not as regular as with Fontinalis, but 

 their agreement is perhaps as close as might be expected 

 when it is noticed that the experiments range over three 



