Jan. IS. 19-5 Changes in Sweet Potatoes During Storage 339 



tion by the analytical methods employed accumulate to a greater extent 

 than usual; or, inasmuch as many of the potatoes showed small rotten 

 spots at the time of the last sampling, it is possible that although these 

 were cut out and the flesh appeared otherwise entirely sound, the 

 enzyms secreted by the fungus had brought about a partial transforma- 

 tion of starch beyond the zone actually invaded by the mycelium. 



DISCUSSION OF RESULTS 



A striking fact brought out in the tables is the high starch content 

 and the low sugar content of the sweet potato immediately after har- 

 vesting. A number of analyses, not here reported, of potatoes dug at 

 different times also showed that freshly dug potatoes contain only small 

 quantities of sugar. However, as soon as the potatoes are dug, a rapid 

 transformation of starch into sugar takes place. A number of experi- 

 ments not given here showed that this sudden transformation of carbo- 

 hydrates takes place over a v.'ide range of temperatures and that even at 

 30° C. the process is so rapid that sugar accumulates in excess of the quan- 

 tity used in respiration, while at any subsequent period the accumulated 

 sugar diminishes at that temperature as a result of respiration. This 

 initial transformation is in such striking contrast with the later less rapid 

 transformation that the two may almost be considered as distinct phases 

 in the carbohydrate metabolism of the roots. It appears that during 

 the period of active growth processes occur which prevent the accumula- 

 tion of sugar in the roots. The elaborated materials from the leaves are 

 almost wholly transformed into starch. The reverse process, which takes 

 place as soon as the potatoes are dug, seems to be associated with the 

 cessation of the flow of materials from the vines to the roots. The influx 

 of materials from the vines therefore seems to determine the direction 

 of the carbohydrate transformation in the growing roots. 



Subsequent to the initial period, the carbohydrate transfonnations in 

 the sweet potato are greatly influenced by temperature. In warm storage 

 there is a'continual accumulation of sugar in excess of the quantity used 

 for respiration during the first part of the storage period. The corre- 

 sponding disappearance of starch leaves no doubt as to the source of the 

 sugar. 



During the latter part of the season the process is apparently reversed. 

 The increase in the percentage of starch and the decrease in the percentage 

 of sugar during this period suggests that during the latter half of the 

 storage season a reformation of starch takes place, such as has been ob- 

 served in twigs and woody stems and in the tubers of the common potato. 



It should be noted, however, that increased respiration during the latter 

 half of the season, during which the temperature of the storage room rose 

 gradually, may account for the loss of sugar. However, the constancy of 

 the total carbohydrates and the increase in the percentage of starch seem 



