226 Ingvar Jorgensen and Walter Stiles. 
(iv.) In the first stage of growth, practically all the reducing 
sugars and about half the sucrose disappear from the leaf during 
the night. As the season proceeds, a less proportion of the sugar 
in the leaf disappears each night. It is especially the hexoses 
which increase in the leaf owing, to this. These results are 
summarised in the following table. 
Table XXXV. 
Seasonal Variations in Carbohydrate Content of Mangold Leaves. 
Date. 
Temp. 
Sucrose. 
Hexoses. 
Pentoses. 
Pentosans. 
Aug. 26-27 
7-2—23-9°C 
1-50—3-11 
0-20-216 
0-36-0-52 
5-19—5.96 
Sept. 10-11 
6-1—10°C 
4-24—8-27 
5-38—8-90 
0-34-0-76 
4-42—5-90 
Oct. 11-12 
-0-6 - 16 l°C 
4-98—9-52 
9-39—12-41 
0-61—0-92 
6-21-715 
The observations made by Davis, Daish and Sawyer on the 
sugars of midribs and petioles, show that these always contain a 
higher percentage of sugars than the leaves, and this percentage 
increases with the season. The hexoses are always much in excess 
of the sucrose, and the ratio of hexoses to sucrose is always much 
greater in the petioles than in the leaf lamina. These results are 
comparable with Parkin’s observations that the sugar content of the 
snowdrop leaf increases from above downwards, and that the ratio 
of hexose to sucrose also increases. The conclusion drawn from 
this by both Parkin and the Rothamsted workers is that sucrose is 
the first sugar formed in the leaf and that this is converted into 
hexoses for translocation purposes. In support of this they also 
adduce the fact that the cane sugar is always present in relatively 
high proportion in the leaf, especially early in the season when it is 
present in excess of the hexoses. They suppose the cane sugar is 
gradually inverted by means of the enzyme invertase which is 
secreted or distributed on the surface of the sieve tubes. 
We have already referred to the unreliable character of the 
determinations of glucose and fructose, an unreliability which is 
quite realised by Davis, Daish and Sawyer. As, therefore, it is not 
at all clear what the quantities they term “ apparent dextrose ” and 
apparent levulose ” really represent, we do not think any useful 
purpose would be served by discussing the values they obtain for 
these quantities. 
