Dec. 20. 191 s Respiration Experiments with Sweet Potatoes 515 



tion, a certain allowance should perhaps be made for the nonconformity 

 of samples, since the sugar content of the sweet potatoes at the beginning 

 of each experiment was necessarily determined in collateral samples. 

 Nevertheless, two facts appear evident. During the course of the ex- 

 periments there was no diminution, but, on the contrary, an increase, in 

 the quantity of cane sugar present in the sweet potatoes, while there 

 was a marked decrease in the reducing sugar in all the experiments 

 except the first. 



The rise in the cane-sugar content of the sweet potatoes is most 

 marked in the first experiment, but in this case the rapid change is simply 

 an example of the generally observed manifestation that the sugar con- 

 tent of sweet potatoes is low while they are in the ground and rises 

 rapidly immediately after they have been dug. In all the other experi- 

 ments, although the increase is small (from 0.08 to 0.6 per cent), the 

 differences all point in one direction. It seems clear, therefore, that 

 there was at any rate no decrease in the cane-sugar content of the sweet 

 potatoes during the course of the experiments. 



This fact indicates that at 30° C. the cane sugar is reformed as rapidly as 

 it is used for respiration or that it does not function in the respiratory 

 processes, at least while other carbohydrates are present in abundance. 

 Which of these possibilities occurs can not with certainty be determined 

 from the data. A number of relative facts, however, seem to point to a 

 rather high degree of stability of the cane sugar in the sweet potato, in 

 so far as the processes of respiration are concerned. It has been found 

 as the result of many analyses that at low temperatures (5° C.) there is 

 an extensive accumulation of cane sugar in the sweet potato and that 

 this increase of sugar takes place at the expense of the starch, which 

 disappears correspondingly. At higher temperatures (15° to 20° C.) the 

 accumulation of cane sugar is much less extensive and, in fact, does not 

 proceed beyond a certain maximum, which, during the season's storage, 

 is reached in March or early April. After the period of sugar formation 

 the starch content of the sweet potatoes remains fairly constant, for the 

 quantity of starch w^hich disappears in respiration compared with the 

 quantity used in the formation of sugar is so small that in view of indi- 

 vidual differences among sweet potatoes and the errors of manipulation 

 it has not been possible to determine the changes in starch content in 

 connection with respiration in experiments carried on for short periods 

 of time. 



These facts seem to indicate that at higher temperatures the produc- 

 tion of cane sugar is depressed. We should therefore expect that if 

 sweet potatoes which have been stored at 15° to 20° C. until the cane- 

 sugar content has attained an equilibrium (March to April) are subjected 

 to a temperature of 30°, the production of cane sugar would be still 

 further retarded or even inhibited. At the same time the rate of respira- 

 tion is accelerated. 



