Dec. 20, 1915 
Respiration Experiments with Sweet Potatoes 
5i3 
gm. The sugar content of these lots was remarkably uniform. Only 
the lot used in the fourth experiment was lower in cane sugar and higher 
in reducing sugar than the rest. In spite of this difference, the respira¬ 
tion in all cases was practically the same, beginning in the neighbor¬ 
hood of 50 mgm. per kilogram per hour and falling to about 40 mgm. 
toward the end of the experiments. In all cases the glucose equivalent 
of the carbon dioxid generated was higher than the loss of reducing 
sugar calculated from the analytical data. 
DISCUSSION OF RESULTS 
A comparison of the sugar content of the sweet potatoes in the differ¬ 
ent experiments with the respiration of the roots shows that no general 
correlation is evident between the total sugar content and the respira¬ 
tory activity. It is true, indeed, that the roots having the highest sugar 
content (third experiment) also had the highest respiration, but these 
sweet potatoes had been subjected to low temperature for a month, and 
it is likely that such treatment induces other changes than those indi¬ 
cated by the carbohydrate transformations, for sweet potatoes thus 
treated become subject to the attacks of certain fungi which ordinarily 
do not readily invade the tissues. Moreover, it appears from experi¬ 
ments of Palladine (10) that, with a plentiful supply of carbohydrates 
present, plant organs which have been exposed for a time to low tem¬ 
perature respire more energetically when brought into a high tempera¬ 
ture than those which have been continually kept at the higher tem¬ 
perature. Furthermore, the carbon-dioxid production in the third 
experiment fell off rapidly until it was no greater than that at the 
beginning of the second experiment, but the total sugar content of the 
sweet potatoes in the third experiment remained at all times much 
higher than that of the roots in the second experiment. The other 
experiments also show no correlation between the total sugar content of 
the sweet potato and the respiratory activity. Thus, the roots in the 
second experiment were low in total sugar, but had a high respiration, 
while those in the fifth, sixth, and seventh experiments had a compara¬ 
tively high sugar content and low respiration. It is possible that irregu¬ 
larities in the size and shape of the sweet potatoes might account for 
differences in respiratory activity, but these sources of error were avoided 
as far as possible by the selection of fairly uniform roots. It is therefore 
unlikely that great differences in respiratory activity can be attributed 
to these factors. 
While there appears to be no evident correlation between the total 
sugar content and the respiratory activity, the case is different when the 
reducing sugar alone is considered. Here there is evidence of a general 
parallelism, which, however, is easily obscured by other factors. This 
correlation is perhaps most clearly brought out by the gradual fall of the 
respiration, with the disappearance of the reducing sugar in the indi- 
