Variations in the Carbohydrate Content. 1 19 



II. Stage of intermediate growth. 10 a.m., September 10 — 

 8 a.m., September 11, 1912. 



III. Pinal stage of growth. 9 a.m., October 11 — 7 a.m., 

 October 19, 1912. 



In each case, the leaves and leaf stalks were treated separately. 

 In the first series the upper and lower parts of the leafstalk were 

 dealt with separately ; in the second series, the midribs of the leaves 

 were subjected to a separate analysis ; in the third stage of growth 

 the midribs and leaf stalks were treated together. Their results 

 are all calculated in terms of the total vacuum dried matter of the 

 leaf. 



It may be mentioned at once that Davis and his collaborators 

 found starch was absent from the leaves and petioles of the mangold 

 at all stages of growth except the very earliest. Similarly, no maltose 

 was ever found in either leaves or petioles of this plant at any time. 

 The quantities of other carbohydrates present in the leaf are 

 indicated in the accompanying figures, which are based on the 

 numbers and curves given in Davis, Daish and Sawyer's paper. 



Fig. 14 shows the variation in content of the sugars of the 

 mangold leaf found during 24 hours on August 26-27, 1913. The 

 most noteworthy features of these results are : — 



1. Both hexoses and sucrose increase rapidly in quantity 

 after daybreak and reach a maximum about mid-day, after which 

 the quantity present falls off fairly regularly and rapidly until the 

 following dawn. Practically the whole of the hexose sugar disappears 

 and about half the sucrose. These changes are closely parallel to 

 the temperature curve (and probably also to the curve of light 

 intensity). 



2. The quantity of sucrose is always greater than that of 

 hexose. 



3. The variations in the quantity of cane sugar are small, the 

 limits being between 3-11% and 1'5%, whereas the hexoses vary 

 between 0-77% and 2-16%. 



4. The quantity of pentosan remains practically constant 

 throughout the day, the fluctuations being probably within the 

 range of experimental error. The same holds for the matter 

 insoluble in alcohol. Davis and his co-workers consider the 

 increase tliey found in the values of these substances to lie really 

 significant, but if this were so, there should be either a sudden fall 

 in these values at sunrise, or the proportion of them in the leaf 

 should go on increasing from day to day. As a matter of fact, in 



