Variations in the Carbohydrate Content. 125 



4. Potato (Solanum tuberosum, vnr. 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 Fig. 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 

 thioughout 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. 



6 S>m«t 10 



2a«. *»«'>** 



Fig. 17. Variation in Content of varioua Carbohydrates in the leaf of 

 Potato during 24 hours, July IG— 17, li)14 (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 staich 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 



