60 



STUDIES IN PLANT EESPIRATION AND PHOTOSYNTHESIS. 



lively greater decrease of glucose than of levulose. While Musa 

 ensente Gruel, which forms very little starch, showed a decrease in 

 cane sugar and maltose during the period of darkness, glucose in- 

 creased and levulose remained the same. The results with Cucurbita 

 ficifolia Bet6 and with Canna viridiflora R. and Pav. are not as definite, 



Table 40. 



but seem also to indicate that in the course of respiration more of 

 the glucose is utilized. The expression of analytical data in terms 

 of percentages of the dry-leaf material makes uncertain the calcula- 

 tion of the amounts of the various sugars used up. 



Table 41. — Rate of emission of CO2 by 9 leaves of Helianihus annuity at 25°. 

 Petioles in nitrogen-free nutrient solution containing 7 per cent levulose. CO2 absorbed in 

 Ba(0H)2 solution, 0.12153 normal, 125 c. c. of which has CO2 equivalent of 0.3343 gram CO2. 



While the evidence is as yet by no means conclusive, it appears 

 that levulose in leaves is more stable than glucose. The question 

 resolves itself into whether d-glucose is actually more easily con- 

 sumed in the leaf or whether d-levulose is, under certain conditions, 

 converted into d-glucose. The problem of the glucose-fructose 

 relation is a very fundamental one in the carbohydrate economy of 



