Carbon Assimilation. 
227 
4. Potato (Solanum tuberosum, var. King Edward VII). 
Davis and Sawyer have made analyses also of the carbohydrates 
of a leaf which forms starch, that of the potato. The samples were 
gathered at 2-hourly intervals, from 6 a.m., July 16th to 4 a.m., 
July 17th, 1914. Separate analyses were made of the stalks. Their 
results are summarised in Pig. 17. It will be observed that sucrose 
is the chief sugar present, as was found to be the case also in the 
early stage of growth of the mangold. The sucrose content of the 
leaves rises during the day until 2 p.m., and then falls off regularly 
until dawn the next day. The hexoses show much variation 
throughout the day and night, and here again it is impossible 
through absence of data, to judge whether these variations are 
anything more than differences due to sampling. The hexose 
content is, on the whole, higher during the day than at night. The 
pentoses show little variation. 
Fig. 17. Variation in Content of various Carbohydrates in the leaf of 
Potato during 24 hours, July 16 — 17, 1914 (After Davis, and Sawyer). 
The starch content shows a decided maximum in the late 
afternoon (6 p.m.) and at the same time a quantity of dextrin 
(soluble starch) is present. By sunset this has almost disappeared 
and the starch content has rapidly fallen. 
As in the mangold, in the leaf stalks of the potato the hexoses 
are much in excess of the sucrose, and it is reasonable to suppose 
