﻿BOTANICAL GAZETTE 



erally conjectured that the after-ripening processes in tubers are 

 metabolic in character; in other words, it has been supposed that 

 chemical changes occur in the tubers during the rest period which 

 render certain essential foods or other materials available for the 

 growing bud. The first problem in the following study was to 

 ascertain if there are metabolic processes occurring in the potato 

 tuber during the rest period which are characteristic of after- 

 ripening, and to determine their character as far as possible. 



The tubers used in this investigation produce sprouts much 

 earlier from the buds on the seed or terminal end when the tubers 

 are left whole. In the majority of cases, the buds on the stem or 

 basal end do not germinate at all unless those on the seed end are 

 injured; therefore, tubers were cut in half at regular intervals 

 during the rest period, and the following analyses made sepa- 

 rately on the seed and stem halves with a view to detecting better 

 the chemical changes characteristic of after-ripening. We are 

 not justified in assuming that all chemical changes occuring in 

 the whole tuber during the rest period must be peculiar to after- 

 ripening. 



Carbohydrates. — In a previous chapter it was stated that 

 storage at low temperature has been claimed to be capable of short- 

 ening the rest period of potato tubers. It has been proved that 

 during such storage sugar accumulates in the tubers. These facts 

 have led to the supposition that the rest period is caused by a 

 deficiency of soluble carbohydrates, and that the cessation of the 

 rest is due to a gradual production of the diastase. In order to 

 determine if carbohydrate transformations are essential after- 

 ripening processes, or simply due to changing temperature, analyses 

 were made during after-ripening of tubers at a fairly constant and 

 favorable growing temperature. At the same time analyses were 

 made on tubers stored under variable low temperature in a potato 

 vault. Samples of 8 tubers, each with a total weight of about 

 one kilogram, were selected from both lots at intervals of 2 and 4 

 weeks. Each tuber was cut into two equal parts, the one part 

 representing the terminal or seed end, the other, the basal or stem 

 end. The seed ends of each sample were all grated together; like- 

 wise the stem ends. After being thoroughly mixed in a mortar, 



