552 Journal of Agricultural Research voi. v,no. 13 



There was a large loss of starch and a great accumulation of sugar during 

 the first period, very little further loss of starch and accumulation of 

 sugar during the second period, and a slight increase in reducing sugar 

 during the first period, with a small loss during the second. But if the 

 data of this experiment are compared with the corresponding data of the 

 first and second experiments, it will be noted that the starch content of 

 the sweet potatoes in the third experiment at the time they were dug is, 

 on the whole, lower than that of the freshly dug potatoes in the first and 

 the second experiments, and the cane sugar is higher, as though a part of 

 the starch had already been converted at the time when the roots were 

 dug. Furthermore, it will be noted that the loss of starch and the incre- 

 ment in cane sugar during the first period are a little less than in the 

 corresponding periods of the first and second experiments. These facts 

 show that as a result of the cutting of the vines the carbohydrate trans- 

 formations had been initiated in these potatoes while they were still in 

 the ground, but that the changes did not proceed as rapidly at the 

 temperature of the soil as at 30°. 



The results of the experiments at 30° C. may be summed up thus: In 

 the freshly dug sweet potatoes whose Amines were intact there was a large 

 loss of starch and increase of cane sugar during the first period of 12 days, 

 and very little further change in these substances during the second 

 period. The changes in reducing sugar are obscured by the active 

 respiration induced by high temperature and wounding, but, on the 

 whole, the data show that there was a more extensive formation of 

 reducing sugar during the first period than during the second. The 

 potatoes which had been left in the ground for some time after the vines 

 had been cut showed the same general phases of change, but their starch 

 content was on the whole lower and their sugar content higher at the 

 time of digging, and the rate of starch conversion during the first period 

 was lower than in the potatoes dug while the vines were still intact. 

 These conditions indicate that the carbohydrate transformations had 

 proceeded to some extent in these potatoes after the vines had been cut 

 and while the roots were still in the ground. 



If the experiments at 5° C. (Table IV) are now examined, a marked con- 

 trast is found between these and the experiments at 30°. In the first 

 two experiments with potatoes whose vines had remained active up to the 

 time of digging, the loss of starch during the first period is much less than 

 at 30°, but the loss continues at approximately the same rate during the 

 second period. With respect to the behavior of the cane sugar the 

 contrast between the potatoes at 30° and those at 5° is equally marked. 

 At 5° there is only an insignificant increase in cane sugar during the first 

 period, but a marked increase during the second. The reverse is true of 

 the reducing sugar. There is a considerable accumulation during the 

 first period and a marked reduction during the second. 



