STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 57 



attributable to the influence of the glycocoll from the nutrient 

 solution, while the rise after 35 hours, which is noticeable in both 

 experiments, represents the effect of the natural accumulation of 

 amino-acids in the leaves, which becomes noticeable even in those 

 leaves which have been given no sugar in the nutrient solution. 



AO 50 60 70 90 



Figure 15. 

 Rates of respiration with sucrose. The broken line indicates the rate of respiration 

 of 6 leaves of Helianihiis annuus at 25°; petioles in nitrogen-free nutrient solution con- 

 taining 7 per cent sucrose. Values taken from table 35. The soUd line indicates the 

 rate of respiraton of 6 leaves of the same plant at 25°; petioles in nitrogen-free nutrient 

 solution containing 7 per cent sucrose and 0.11 per cent glycocoll. Values taken from 

 table 37. The ordinate represents mg. CO2 per hour per gram dry material, the abscissa 

 time in hours. 



5. d-levulose. 



As was pointed out in the introductory discussion, the purely 

 chemical experiments of Nef, as well as the physiological studies of 

 Lusk, point to the conclusion that d-levulose is more easily oxidized 

 than any of the other hexose sugars. Among plants, particularly 

 the lower ones, there is a great diversity in the capacity for using 

 different sugars. There exists little information on the relative 

 value of the various sugars in respect to respiratory activity of 

 higher plants. Palladin^ attempted to determine the influence of 

 various sugars on the rate of respiration. He found that d-levulose 

 produced a greater carbon-dioxid emission than either d-glucose, 

 sucrose, maltose, raffinose, glycerine, or mannit. However, Palladin 

 worked with etiolated bean shoots. These were placed in solutions 

 of the various sugars for 2 to 4 days and then the rate of respiration 



1 Palladin, W. Rev. Gen. de BoL, 13, 19, 93, 127 (1901). 



