THE CARBOHYDRATES OF THE ANGIOSPERM LEAF 29 



from 50 grammes of chopped-up leaves, which was evapor- 

 ated down to about 20 c.c. The great liability to hydro- 

 lysis of sucrose under these conditions has been pointed out 

 by C. A. Browne (1912). This error would vary with the 

 time occupied by each extraction, and would lower the 

 sucrose content and raise that of the hexoses. Bearing in 

 mind this possible source of a fluctuating error, it remains 

 to consider the results obtained, which are of great interest. 



Leaves were collected every two hours of the twenty-four 

 in the middle of September. The quantities of carbo- 

 hydrates found are recorded in Tables XVII. and XVIII., 

 from which the graphs have been constructed. 



From the tables and graphs it is seen that the hexoses 

 do not appear to fluctuate very much, but there is an 

 approximately constant percentage throughout the day, 

 and a somewhat lower percentage during the night. The 

 curve rises suddenly between 4 a.m. and 6 a.m. (sunrise 

 being at 5-30 a.m.), and falls between 6 p.m. and 8 p.m. 

 This points to a quick response of the leaf towards light, 

 shown by hexose formation. The constant level at night 

 seems to indicate that the hexoses are not largely concerned 

 in translocation. 



The sucrose varies from about 0-5 to 2-5 per cent. The 

 rise begins about sunrise, and continues till sunset, when 

 there is a rapid fall. The curve, however, lags behind that 

 of the hexoses by about an hour. 



It is also found that the starch varies much in the same 

 way as sucrose, though its curve lags slightly behind that 

 of the latter in the morning, and continues to rise till mid- 

 night. As to its formation during darkness two views must 

 be considered that it arises from (a) the hexoses, thus 

 producing the fall to their night level, and from the 

 hexoses originating from inversion of the sucrose; 

 or (6) the sucrose present at nightfall, together with 



