[Vol. 6 

 232 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



The diastatic activity of both potato and onion leaves was 

 determined by Brown and Morris ('93) and by Bradley and 

 Kellersberger. Thus it is possible to compare, by means of the 

 values given for onion leaves, the activities of the potato leaves 

 as found in the two cases. Different units, of course, are used 



the enzyme activity in the 



Ilelative diastatic activity 



Determination made by Potato leaves Onion leaves 



Brown and Morris 8.2 3.80 



Bradley and Kellersberger 75.0 1.05 



It is seen from the above that the relative activity in the case 

 of the potato, as found by Bradley and Kellersberger, was much 

 higher than that found by Brown and Morris. This is doubtless 

 partly due to the fact that the former authors made their 

 determinations by means of the cupric-reducing power of the 

 solutions, while the latter employed the iodine reaction. It 

 illustrates the wide difference that often occurs in the results 

 obtained by different workers along this line. In this case, 

 however, the difference is not one of direction, but of degree only. 



The physiological changes taking place in the potato during 

 its rest period have been studied to a considerable degree by 

 Appleman ('11, '16). He found, as did Miiller-Thurgau and 

 others, that glucose and sucrose accumulate in potatoes which 

 are stored at 0° C. Diastase activity was also greater at the 

 end of 2 and 4 weeks in the cold-storage potatoes than in those 

 stored at room temperature, but at the end of 6 weeks practically 

 no difference could be detected, as, he explains, this was near the 

 end of the rest period of the variety used in this work. Apple- 

 man ('11) says that "the increased diastatic activity is prob- 

 ably due to greater activation of zymogen by free acids which 

 are liberated by the greater permeability of protoplasmic mem- 

 branes at low temperatures." 



It is well known that potatoes will not germinate for several 

 weeks after being harvested, apparently because certain changes 

 known as "after-ripening" must lirst take place. In attempt- 

 ing to determine the nature of these changes, Appleman ('16) 

 reached the conclusion that carbohydrate transformations in 

 the potato tuber during its rest period must not be considered 



