STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



59 



equal quantities of dextrose and levulose. There was thus un- 

 doubtedly a preponderance of dextrose. Nevertheless, there was a 

 much greater increase of levulose than of dextrose during the 24 



Table 38. 



hours the leaves were in the dark. Brown and Morris calculate 

 from these results that far more dextrose than levulose is used in 

 the respiratory process, as is shown in table 39. 



Table 39. — Stigars used up in respiration 

 expressed as percentages of the dry-leaf 

 material. 



The work of Parkin* substantiates the conclusions of Brown and 

 Morris. Working with Galanthus nivalis, the leaves of which do 

 not store starch, Parkin found that levulose, as a rule, is in excess 

 of glucose, irrespective of the time of day the leaves are taken for 

 analysis. 



"Out of 52 duplicate leaf analyses made, 47 had the fructose in excess of the glucose, 

 and only 7 the reverse. Representing fructose as unity, in the former cases the ratio 

 varied from 1 : 0.4 to 1 : 0.76, and in the latter from 1 : 1.01 to 1 : 1.06. The calculation 

 of the separate amounts of glucose and fructose depends chiefly upon one observation, 

 viz, the optical angle of rotation. A slight error in the reading of this will affect 

 the results considerably; consequently it might hardly be expected that any further 

 conclusion beyond the bare fact of the excess of one hexose sugar over the other 

 could be reached." 



A later investigation of the carbohydrates of foUage leaves by 

 Gast^ yielded very similar results. Tropceolum niojus and Vitis 

 vinifera during 24 hours of respiration in the dark showed a rela- 



1 Parkin, J. Biochem. Jour., 6, 1-47 (1911). 



2 Gast, W. ZeU. physiol. chem., 99, 1-53 (1917). 



