﻿iqi6] APPLEM AN— REST PERIOD 277 



this and the nitrogen precipitated by tannic acid, the proteose, and 

 the peptone nitrogen. The nitrogen not precipitated by phospho- 

 tungstic acid was considered the nitrogen of monoamino acids and 

 their amide derivatives, while the difference between this and the 

 nitrogen not precipitated by the tannic acid was considered the 

 nitrogen of diamino acids and other bases. It is not claimed that 

 the foregoing precipitation method gives absolutely the true pro- 

 portion of nitrogen in the various forms of binding, but it yielded 

 valuable comparative results under the conditions employed in the 

 determinations. 



The nitrogen determinations were made on Green Mountain 

 potatoes harvested on November 4 and planted at once in wet 

 sawdust on the floor of the greenhouse. The temperature varia- 

 tion in the sawdust was slight and the tubers were constantly under 

 favorable growing conditions. Sprouts began to appear on this lot 

 of potatoes on January 19. The set. of analyses made on January 18 , 

 therefore, shows the nitrogen situation just at the end of the rest 

 period. The tubers used for the last set of analyses bore sprouts 

 from one-eighth to one inch in length. As soon as sprouting began, 

 the tubers were placed in a moist chamber, which was buried in 

 the sawdust; therefore nothing was absorbed by the roots except 

 possibly a little water. Each sample contained 6 tubers with a 

 total weight of about 800 gm. The variation in total weights was 

 not more than 5 gm. The samples were all weighed the day after 

 the potatoes were harvested, and kept separate during the storage 

 in the wet sawdust. This makes possible the calculation of results 

 to percentage of original weight, and thus apparent changes due 

 to loss in dry substance through respiration and also through 

 changes in water content are avoided. 



On the above basis of calculation the different forms of nitrogen 

 in the whole tuber showed no general change until the tubers began 

 to sprout. During the rest period the stem half always showed a 

 higher percentage of nitrogen, calculated to percentage of total 

 nitrogen, in the following forms: monoamino acids and amides, 

 diamino acids and other bases, proteoses, and peptone. The seed 

 half contained a slightly higher percentage of both water-soluble 

 and water-insoluble protein nitrogen (tables IX-XI). The slight 



