1911] APPLEMAN—AFTER-RIPENING OF POTATO 307 
occurring in the potato tuber as after-ripening proceeds during 
Storage ato’ C. It is intended to throw some light upon the nature 
of the limiting factor or factors of growth during the rest period 
of this particular organ. Thus far a quantitative study has been 
made of digestive and respiratory enzyme changes and the carbo- 
hydrate food transformations. 
Material 
The material used for this investigation was the red land 
potatoes grown in Texas and procured only a few days after 
being harvested. This variety has a very short rest period. Two 
crops a year are grown in this climate, and samples from both 
crops were used in this work. The tubers were wrapped with 
paraffin paper and one-half stored at o° C. and the remainder 
stored in a dark basement room at 20-25° C. 
Methods 
GLUCOSE, SUCROSE, AND STARCH.—The methods employed for 
the determinations of glucose, sucrose, and starch were virtually 
those of the association of official agricultural chemists (7). The 
glucose was determined according to the method of Munson and 
WALKER. 
Diastase.—A modification of the starch iodine method (8, 9) 
was used in making the diastase determinations. One cc. of a 
I per cent soluble starch solution was placed in each of ro test 
tubes surrounded with ice. Ascending amounts of the potato 
extract, prepared’ by grinding with quartz sand and filtering, were 
added to the tubes, beginning with 1 cc.-and increasing the amount 
©.1 cc. for each succeeding tube. The tubes were then incubated 
at 40° C. for 48 hours, placed again in ice, filled nearly full with 
water, and 3 drops of iodine solution added to each tube. The 
first tube in the descending series which showed a blue or violet | 
color was considered the index for comparative diastatic activity. 
The method is impractical with larger amounts of extract on 
account of dark oxidation products and the precipitate which 
falls on addition of the iodine. If small amounts of both starch 
solution and extract are used, and the incubation continued for 
