5i6 Journal of Agricultural Research voi. v. no. 12 



If no more cane sugar is formed and its utilization is hastened, we 

 should expect a reduction in the quantity of cane sugar, at least in the 

 experiments at the end of the season, if that substance is used in respira- 

 tion. Such a reduction, however, occurs neither at the end of the 

 season nor at any other time. It appears not unlikely, therefore, that 

 the cane sugar in the sweet potato is relatively stable, with respect to 

 the respiratory processes. 



Although there was no diminution of cane sugar in the sweet potatoes 

 used in these experiments, there was a marked decrease in the reducing 

 sugar in all cases except the first. The first experiment, in which freshly 

 dug roots were used, is exceptional for the reason mentioned above. 

 It shows that in freshly dug roots the processes of sugar formation are 

 so rapid that even at 30° C. sugar is formed faster than it is used in respira- 

 tion. In this instance an amount of carbon dioxid equivalent to 27.45 

 gm. of glucose was evolved during the experiment, and in addition to 

 this there was an increment of 9.77 gm. of reducing sugar, as calculated 

 from the percentages present in the sweet potatoes at the beginning and 

 at the end of the experiment. In all the other experiments there was a 

 decrease of reducing sugar — i. e., the quantity of reducing sugar which 

 had accumulated while the sweet potatoes were stored at low tempera- 

 tures was diminished when the roots were subsequently exposed to a 

 higher temperature. It is reasonable to infer that the sugar was utilized 

 in respiration, but it will be observed that in all but the first and second 

 experiments the loss of reducing sugar calculated from the percentages 

 at the beginning and at the end of the experiments accounts only for a 

 portion of the sugar equivalent to the quantity of carbon dioxid evolved. 

 The deficiency is no doubt made up by the transformation of starch, for, 

 as Deleano (3) found in the case of grape leaves cut from the vines, the 

 starch functions readily in the respiratory processes. In the sweet 

 potato the starch appears to be even more readily available than the 

 cane sugar. In the second experiment, where the invert-sugar content 

 was high at the beginning of the experiment, a synthesis of other carbo- 

 hydrates may perhaps be assumed. 



CONCLUSIONS 



The experiments described in this paper seem to indicate that there 

 is no general correlation between the total sugar content of the sweet 

 potato and its respiratory activity. A simultaneous decrease in the 

 reducing-sugar content and the respiratory activity of given lots of roots 

 indicates a correlation between reducing-sugar content and respiration, 

 but seasonal changes and environmental conditions to which the sweet 

 potatoes have been previously subjected tend to obscure any such corre- 

 lation in different lots. Experiments with wounded roots indicate that 

 the sugar content is not the limiting factor in the respiration of the 

 sweet potato. The reducing sugars are the immediate source of respira- 



