332 Journal of Agricultural Research voi. iii, N0.4 



That the periodic transformation of reserve starch is not restricted to 

 the stem tissues of plants is shown by the observations of Haberlandt 

 (1876), of Mer (1876), and of Schulz (1888), who found that the starch 

 disappears from evergreen leaves in temperate regions in winter, while 

 Haberlandt and Schulz noted also that it was re-formed in spring. The 

 most thorough investigation of the carbohydrate transformations in ever- 

 green leaves was made by Lidforss (1907), who found that the leaves of 

 all evergreen plants in cold countries, except aquatic plants, lose their 

 starch in winter, sugar appearing in its place, and that starch is regen- 

 erated in the leaves in February and March when the temperature scarcely 

 rises above 5° C. 



That similar changes occur in the subterranean parts of perennial 

 plants in temperate regions was shown by Rosenberg (1896), who 

 obser\'ed the disappearance of starch after leaf fall in the subterranean 

 parts of Spiraea nlmaria, Scrophidaria nodosa, Plantago major, Poicntilla 

 argentea, and Hepatica triloba, but did not determine what substances 

 appeared in its place. By far the most complete account of carbohydrate 

 transformations in dormant organs of this type is given by Miiller- 

 Thurgau (1S82) in his classical researches on the accumulation of sugar 

 in the potato (Solanum tuberosum) and other plant organs at low tem- 

 peratures. Miiller-Thurgau found that an accumulation of sugar and a 

 corresponding loss of starch occurred in potatoes kept at low temperatures 

 (0° to 6° C), while, contrary to popular opinion, no sugar is formed in 

 potatoes which have been actually frozen. He found that when potatoes 

 which had become sweet as a result of exposure to low temperature are 

 kept at a higher temperature (8° to 10° C.) the sugar disappears and the 

 starch increases. Furthermore, he showed that the sugar formed con- 

 sists mostly of reducing sugar with some cane sugar in the proportion of 

 about 2.5 to I, and that similar transformations occur in other parts of 

 plants. These phenomena are interpreted by Miiller-Thurgau (1882) as 

 follows : 



The transformation of starch into sugar is an enzymic process which, 

 although more rapid at high temperatures, occurs also at low tem- 

 peratures. The respiratory activity which is almost at a standstill 

 at 0° C. rises with the temperature so that at higher temperatures 

 an increasingly greater amount of sugar is consumed by respiration. 

 The amount of sugar used in respiration at higher temperatures is, 

 however, small compared with that utilized by another process — i. e., 

 the re-formation of starch from sugar, which takes place at tempera- 

 tures somewhat above 0° C. and increases in speed with the rise of 

 temperature. Appleman (1914) in his studies on the rest period of the 

 potato also finds that the carbohydrate changes in the dormant tubers 

 are entirely dependent upon changes of temperature. It appears, there- 

 fore, that the carbohydrate transformations of the potato, although a 



