Dec. 27. 191S Carbohydrate Transformations in Sweet Potatoes 559 



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 sugar, as has been observed 

 in cotyledons and 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°. These data show that 

 during these periods the loss of starch and the gain in sugar was greater 

 at 5° 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°, but the reaction obvi- 

 ously approaches an end point which is more rapidly approximated at 

 30° than at 5°; hence, the reaction slows down more rapidly at 30° than 

 at 5°. 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°, 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°. At 5°, 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 

 12573°— 15 2 



