126 



TEXTBOOK OF BOTANY 



necessary to find out how the CO2 and H2O are united, whether they 

 unite with the chlorophyll molecule, how the enzyme enters into the 

 process, and what products are formed first as the chlorophyll and 

 enzyme are again set free. It is impossible at present to say how many 

 intermediate products are formed, and how many enzymes catalyze 

 their formation. 



Rate of photosynthesis. From the foregoing discussion it should be 

 evident that the rate of photosynthesis is influenced by many conditions 

 within the plant and by several environmental factors. Attention has 

 been called to some of the influences of the stomates, intercellular spaces, 

 distribution of chlorophyll, activity of enzymes, light, temperature, car- 

 bon dioxide, and water. Other conditions, such as the amount of 

 chlorophvll and possibly the acidity of the cells, also influence the rate of 

 photosynthesis. The effect of any one factor is probably always influenced 

 to some extent by the relative amounts of the other factors involved. 

 Some idea of this fact is best obtained by studying the results of experi- 

 mental data such as those represented bv the accompanying curves. 



20 'yo 40'7o 60«7o 60«7o 



UGHT INTENSITY IN PER.CENTS OF FULL SUNUGHT 



IOO«To 



Fig. 

 of 



57. Rates of photosynthesis in relation to light intensity and the concentration 

 carbon dioxide. Data from W. H. Hoover, E. S. Johnson and F. S. Brackett. 



The curves in Fig. 57 indicate the relative rates of photosynthesis in 

 wheat seedlings in relation to light intensity and the concentration of 

 carbon dioxide in the air, when the temperature is 22° C. and the rela- 



