Dec. 27,1915 
Carbohydrate Transformations in Sweet Potatoes 
55 9 
would, therefore, be correlated with that of the starch. From these con¬ 
siderations it appears that the hydrolysis of starch in the sweet potato 
results directly in the formation of reducing su^ar, as has been observed 
in cotyledons^Lnd other living plant organs, and that the cane sugar is 
synthesized from the reducing sugar. Cane sugar is therefore the end 
product of this series of carbohydrate transformations. 
It has sometimes appeared from the extensive accumulation of cane 
sugar in plant organs at low temperatures that this process went on 
more rapidly at low than at high temperatures. Such a conclusion 
would seem to be justified if later phases of the process were compared 
at different temperatures, as illustrated by the data relating to the sec¬ 
ond periods of the experiments at 30° and at 5 0 . These data show that 
during these periods the loss of starch and the gain in sugar was greater 
at 5 0 than at 30°. On the basis of the interpretation given above, how¬ 
ever, it is clear that all these reactions conform in general to the Van’t 
Hoff temperature rule regarding chemical reactions. Thus, the rate of 
conversion of starch is higher at 30° than at 5 0 , but the reaction obvi¬ 
ously approaches an end point which is more rapidly approximated at 
30° than at 5 0 ; hence, the reaction slows down more rapidly at 30° than 
at 5 0 . It is evident also that the production of cane sugar is more rapid 
at higher temperatures, and that the reaction, which is prolonged at 
5 0 , nears an end point more quickly at 30°. Hence, if these reactions at 
different temperatures are compared in their later phases, they will appear 
to be more rapid at the lower temperature. In the common Irish potato 
as well as in some other living plant organs, the series of reactions re¬ 
sulting in the production of cane sugar from starch has been found to be 
reversible. It is not unlikely that in the sweet potato also the reaction is 
reversible and that thus the attainment of a final equilibrium between 
the starch, reducing sugar, and cane sugar is explained. The end point 
of the reaction or the point of equilibrium is greatly shifted with change 
of temperature, with the effect that at low temperatures the system 
permits a greater concentration of sugar than at higher temperatures. 
On the basis of these considerations a rational interpretation can be 
given of the rapid initial carbohydrate transformations, which have been 
mentioned several times and which it was in part the object of this work 
to study more fully. The fact that there is a comparatively rapid trans¬ 
formation of starch to cane sugar in sweet potatoes during the first few 
days after they have been dug and a very much slower transformation 
subsequently is supported by the data of the experiments conducted at 
30° and at 15.5 0 . At 5 0 , however, the disappearance of starch continues 
at about the same rate during both periods, while the rate of accumula¬ 
tion of cane sugar is low at first and higher afterwards. All these facts 
are explicable by the interpretation given above. We have to do here 
with processes whose rate depends on the temperature and which at 
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