STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 63 



A comparison of the results of the foregoing three experiments 

 as presented in jfigure 16 shows at once that apparently d-levulose 

 does not produce an increased respiratory activity in Helianthus 

 leaves. Also, the graphs of the rates of respiration differ considera- 

 bly from the experiments in which d-glucose and sucrose were fed 

 the leaves. Of these sugars, d-levulose seems to produce the least 

 active respiratory activity and d-glucose the most active, while 

 sucrose lies midway between the two. In none of the experiments 



J I L 



to 20 30 4C SO CO 70 80 



Figure 16. 

 Rates of respiration with d-levulose. The dotted line indicates the rate of respira- 

 tion of leaves of Helianthus annuus at 25°; petioles in a nitrogen-free nutrient solution 

 containing 7 per cent d-levulose; values from table 41. The broken line indicates the 

 rate of respiration at 25° with a nitrogen-free solution containing 7 per cent d-levulose 

 and 0.11 per cent glycocoU, as per table 43. The soHd line indicates the rate of respi- 

 ration at 25° with a nitrogen-free nutrient solution containing 7 per cent d-levulose and 

 0.138 per cent asparagine. The ordinates represent mg. CO2 per hour per gram dry 

 material , and the abscissa the time in hours. 



with Helianthus leaves in which these sugars alone were given was 

 the initial sugar-content maintained. However, the reduction in 

 all these cases was about the same, as was also the approximate 

 increase in relative water-content. Nevertheless, these sugars show 

 decided variation in their effect on respiratory activity. Moreover, 

 the influence of adding amino-acids to the nutrient solutions con- 

 taining either d-glucose, sucrose, or d-levulose is very different. 

 With d-glucose the effect is marked, particularly before the fortieth 



