1919] 



MCGINTY — DIASTASE ACTIVITY OF SOLANUM TUBEROSUM 237 



and the subsequent synthesis of cane sugar from these. The 

 formation of sugars was observed to be rapid at a high tempera- 

 ture (30° C), more gradual at temperatures of 11.7-16.7° C, 

 while lowering the temperature to 4° C. again accelerated the 

 process. 



Hasselbring and Hawkins ('15) also found, in the course of 

 further experiments, that the carbohydrate content of the two 

 halves of a potato, which had been split longitudinally, was 

 not the same in all cases. While the analyses of the two halves 

 of a freshly dug tuber agreed closely, differences of from 1 to 16 

 per cent were found in corresponding halves of tubers which had 

 been kept for a time. These differences were found regardless of 

 the temperature at which the potatoes had been kept. These 

 authors consider their work to confirm and extend the investiga- 

 tions of Keitt, referred to previously. 



The extensive work of Davis, Daish, and Sawyer ('16) on the 

 carbohydrates of the mangold leaf, and that of Davis and Sawyer 

 ('16) on the carbohydrates of potato leaves are perhaps the most 

 recent contributions along this line. These investigators not 

 only secured much valuable information regarding distribution 

 of sugars and starch at different hours of the day in the leaves 

 mentioned, but also developed methods for the quantitative 

 determination of these substances in plant material. These 

 methods, while they may, according to Jorgensen and Stiles 

 ('17), be subject to certain errors, are doubtless the most reliable 

 to be found at the present time. 



Some of the results obtained in this work were as follows: 

 (1) Starch was found to be entirely absent from mangold leaves 

 except in the early stages of growth, and maltose was never 

 present, either in the leaves, stalks, or midribs, at any time of the 

 day or night. (2) Sucrose was present in the leaf in excess of 

 hexoses in the early stages of growth, but later, when sugar was 

 being stored in the root, the hexoses predominated. The latter 

 sugars were also more abundant than sucrose in the midribs and 

 leaf-stalks. Sucrose was therefore concluded to be the first 

 sugar formed in photosynthesis, being transformed into hexoses 



for the Durnose of 



found to form 



a small proportion of the sugars in the tissues. (3) The 



