60 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



role in the respiratory activity. In the experiments with d-mannose 

 the glycocoU which was given in the nutrient solution had apparently 

 very little effect, as the normal accumulation of amino-acids in the 

 leaf in this case was so very great. There must, of course, also be 

 Umits beyond which there is little increase in amino-acids and above 

 which the rate of respiration does not rise, so that further addition 

 of an amino-acid would be of little consequence. 



Table 49. — Rate of emission of 8 leaves of Helianthus annuus at 25°. 

 Petioles in nitrogen-free nutrient solution containing 7 per cent d-mannose -f- 0.11 per cent 

 glycocoU. CO2 absorbed in Ba(0H)2 solution 0.12153 normal, 125 c. c. of which has the CO2 

 equivalent of 0.3343 gram CO2. 



7. Effect of the Natural Increase in Amino- Acids. Influence of Light 

 on Amino-Acids and Effect on Respiration. 



In the experiments which have been described attention has 

 repeatedly been called to the rise in the rates of respiration after 

 about 35 or 40 hours. An examination of the graphs shows this 

 rise in practically all of the experiments, and particularly is it 

 noticeable in the cases in which no amino-acid was contained in 

 the solution. It is perhaps unnecessary to point out that these 

 graphs do not represent the true course of respiratory activity, for 

 the points in the curves represent the rates of carbon-dioxid emission 

 during a certain period, usually 6 hours. Naturally such an experi- 

 mental procedure makes the variations appear much more abrupt 

 than in all probability they are, so that the rise in respiration rate 

 between the thirty-fifth and fortieth hour must be regarded with the 

 foregoing in view. 



When excised Helianthus leaves are kept in the dark, with the 

 petioles in nitrogen-free nutrient solution (table 16), there is a gradual 



