STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



67 



rise in the amino-acid content of the leaves. Our experiments indi- 

 cate that amino-acids have a stimulating effect on the respiratory- 

 activity of leaves containing the natural sugars, or when they are fed 

 d-glucose or sucrose. It seems permissible to assume that the amino 

 acids which accumulate in the leaves when kept in the dark would 

 exert a similar stimulating effect if the leaves contained sufficient 



40 50 60 70 80 



Figure 17. 

 Rates of respiration with d-mannose. The broken line indicates the rate of res- 

 piration of 8 leaves of Helianthus at 25°; petioles in a nitrogen-free nutrient solution 

 containing 7 per cent d-mannose, values taken from table 47. The solid line indicates 

 the rate of respiration of 8 leaves of Helianthus at 25° with petioles in a nitrogen-free 

 nutrient solution containing 7 per cent d-mannose and 0.11 per cent glycocoU, values 

 taken from table 49. The ordinate represents mg. CO2 per hour per gram dry material, 

 the abscissa the time in hours. 



sugar. Normally, of course, when excised leaves are kept in the 

 dark, besides an accumulation of amino-acids there is a rapid reduc- 

 tion of the sugar-content, so that any stimulating effect of the 

 accumulating amino-acids could not be exerted on account of the 

 reduced fuel material. 



If, however, after the leaves have remained in the dark for a 

 time and the amino-acids have accumulated, glucose is then fed, the 



