THE NATURE OF PHOTOSYNTHESIS 



135 



synthesis is of limited value either because the effect of other factors as 

 light and carbon dioxide-concentration, were not fully recognized or on 

 account of inadequate methods of measuring the temperature and the 

 photosynthetic rate.^^^ 



A second, very important element of the effect of temperature on 

 photosynthesis is that this is greatly influenced by time. At high tem- 



Fig. 13. — Influence of temperature and time on tlie rate of photosynthesis. 



(From Duclaux.) 



peratures a leaf can maintain a maximal rate of photosynthesis only for 

 a short time. The higher the temperature the shorter is the time the 

 maximal rate can be maintained and the steeper is the slope of its de- 

 cline. As a consequence the rate of photosynthesis at higher tempera- 

 tures is not the same during two successive hours and the maximum value 



"'Kreusler, U., Landw. Jahrb., 16, 711 (1887). 



