THE PHOTOSYNTHETIC CURVE 



117 



years, and that identity for this value in successive experi- 

 ments depends on repeating identically intense stimulation 

 of an identical area of leafy tissue. The intensity of 

 illumination varies with the square of the distance of the 

 chamber from the light, and this had to be adjusted for each 

 experiment but could not be measured directly, as the bath 

 window and cooling screen intervened. An error of a few 

 millimetres may have occurred, and the light must have 



10 SO SO 40 SO 



CO2 tftmeentratum in maim per toocc. 



Fig. 34. Curve of Photosynthesis of Elodea under Variation of 

 C0 2 concentration (after Blackman) 



The crosses represent the points in the curve, the dotted line being 



the mean curve. 



varied from changes in the efficiency of the mantles. The 

 uniformity of the area illuminated, 137 sq. cm., depends upon 

 careful packing and distribution of the green shoots upon 

 the silver grid ; this was always covered as completely as 

 possible, and the error from this cause is probably not great.' 1 

 My results show that the top of the photosynthetic curve 

 rounds off gradually after the turning-point, and is never 

 abruptly horizontal as in the curve obtained by Blackman. 

 No conditions could have been more ideally perfect than in 



1 Blackman and Smith, Proc. Roy. Soc, B, 1910, pp. 392, 410. 



