PHYSIOLOGICAL CHANGES IN SWEET POTATOES 

 DURING STORAGE 



By Heinrjcu Hasselbring and LoN A. Hawkins, Plant Physiologists, Plant 

 Physiological and Fermentation Investigations, Bureau of Plant Industry 



INTRODUCTION 



In resting storage organs of plants growing in northern and in tem- 

 perate regions, carbohydrate transformations involving the disappear- 

 ance of reserve starch during the colder months and its temporary reap- 

 pearance in spring have been found to be of general occurrence. The 

 disappearance of starch from the cortex of trees in winter and its reap- 

 pearance in early spring was first noted by Miiller (1877),' who believed the 

 absence of starch in the cortex resulted from its migration into the wood. 

 Russow's investigations (1882-83), which included the examination 

 of a number of tropical and subtropical greenhouse plants, showed that 

 the total or partial disappearance of starch from the cortex of woody 

 plants in winter was a phenomenon of widespread occurrence. He found, 

 however, that the starch did not migrate into the wood, as Miiller sup- 

 posed, for when pieces of cortex chiseled from trunks of trees were kept 

 at a temperature of 14° to 17° R. (17° to 21° C.) starch grains began to 

 reappear in 20 hours. In the tissues which were free from starch in win- 

 ter he found oil and fats. He observed a correlation between the tem- 

 perature and the disappearance and reappearance of starch, but since the 

 processes occurred also in tropical plants in the greenhouse, he did not 

 regard temperature changes or climatic conditions as the prime causes of 

 the observed transformations. Later Grebnitzky (1884) and Baranetzky 

 ( 1 884) showed that the starch of soft- wooded trees disappeared entirely from 

 the wood, cortex, and rays in winter, and that oil appeared in its place, 

 while in hardwood trees the starch disappeared from the cortex, but per- 

 sisted in the wood. Fischer (1891), in his extended investigations on the 

 physiology of woody plants, fully confirmed the observations of Russow 

 (i 882-83) , Grebnitzky ( 1 884) , and Baranetzky (i 884) regarding the appear- 

 ance of oil in place of starch in soft-wooded trees, and showed further that 

 in hardwood trees glucose and tannin are present in the cortex after the 

 disappearance of the starch, and that the glucose, but not the tannin, 

 disappears when starch is regenerated. He found that the regeneration 

 of starch takes place at a temperature only a few degrees above 0° C. 

 The minimum temperature at which he observed the regeneration of 

 starch in twigs was about 5° C, while at 10° to 20° the process went on 

 very rapidly. 



' Bibliographic citations in parentheses refer to "Literatme cited," p. 341. 



Journal of Agricultural Research, Vol. III. No. 4 



Dcpt. of Agriculture, Washington. D. C. Jan. 15. 1915 



(33^) G-" 



