Dec. 97. igis Carbohydrate Transformations in Sweet Potatoes 



551 



In connection with the changes in reducing sugar the effect of cutting 

 on the behavior of the potatoes must be considered. One of the most 

 pronounced effects of wounding plant organs is a stimulation of respira- 

 tion. The respiration of sweet potatoes is nearly doubled when they are 

 spUt longitudinally, and the effect, though decreasing, extends over many 

 days. By reason of this increased respiration split potatoes consume a 

 much larger part of their reducing sugar than do whole potatoes. Never- 

 theless, in spite of this excessive respiration, there was, on the whole, 

 during the first period a slight increase in reducing sugar, which is signifi- 

 cant in comparison with the distinct loss during the second period. It 

 appears clear, therefore, that more reducing sugar was formed during the 

 first period than during the second; for during the first period the pro- 

 duction of reducing sugar kept pace with its utilization, while during the 

 second period the production was not sufficiently rapid to compensate for 

 the quantity used. 



Further evidence that more reducing sugar is formed in the potatoes 

 during the first period than is indicated by the figures in the difference 

 column is furnished by the whole potatoes stored with the first set of 

 halves and split at the end of the first period. The percentage of reducing 

 sugar in these "a" halves of the second period is much greater than in 

 the "b" halves of the first period, with which they are comparable as to 

 time of storage. Unfortunately, there is no such control for the behavior 

 of the halves stored during the second period. 



The potatoes used in the third experiment at 30° C. were allowed to 

 remain in the ground for 15 days after the vines had been destroyed. 

 They may therefore be considered to have been in "storage" in the 

 ground during that period. The temperatures during that time, as given 

 by observations of the United States Weather Bureau at Washington, 

 D. C, were as follows: 



If the cutting of the vines has any effect on the carbohydrate transfor- 

 mations in the roots, the initial changes in these potatoes would have 

 been inaugurated during the period after the vines had been cut and 

 while the roots were still in the ground. However, the changes in these 

 followed the same general course as those in the freshly dug potatoes. 



