THE NATURE OF PHOTOSYNTHESIS 



121 



Treboux (cited above) and of Pantanelli ^"^ on the basis of limiting 

 factors; these seem to lend considerable substantiation to the theory. 

 It is necessary to bear in mind that Blackman and Smith's ^"'^ experiments 

 were the first in which a conscious effort was made to test out this 

 conception of the influence of environmental factors. The method used 

 for determining photosynthetic activity was new and the results from which 

 the final curves were plotted were taken from experiments ranging over 

 three years. 



Fig. 9.— The rate of photosynthesis at different concentrations of carbon dioxide. 

 The ordinate represents the rate of photosynthesis, the abscissa the concentra- 

 tion of carbon dioxide. (Constructed from values given by Warburg.) 



Within recent years conceptions differing from those of Blackman 

 have been advanced by a number of investigators. These modifications 

 of Blackman's views are largely the result of careful experimentation 

 with a variety of different plants and improved means of measuring photo- 

 synthetic rates. 



In 1919 Warburg"" devised a method of determining the rate of 



*»» PantaneUi, Jahrb. f. n'iss. Bot., 39, 167 (1903). 

 ^Blackman and Smith, Froc. Ro\. Sac, 83 B, 374 (1911). 

 ""Warburg, Biochem. Zeit.. 100, 230 (1919). 



