1919] 



MCGINTY — DIASTASE ACTIVITY OF SOLANUM TUBEROSUM 233 



after-ripening processes, but simply due to, and dependent upon, 

 changing temperature. He did not find an increase at the time 

 of sprouting in the reducing or total sugars in the case of potatoes 

 which, since harvesting, had been stored under growing condi- 

 tions; nor was there any difference in the sugar content of the 

 seed and stem ends of the tubers at the beginning of sprouting. 

 The diastase activity, he states, was uniformly greater in the 

 extract from the seed end, but there was no appreciable increase 



■ 



in diastatic activity in either end during the rest period, in spite 

 of the fact that sprouting begins much earlier in the seed end. 



>> 



From this evidence, the conclusion is reached that the "cessa- 

 tion of the rest period is not due to a gradual increase in dia- 

 static activity. 



Appleman ('16) found further that sprouting could be brought 



about at any time during the rest period by removing the skins 



of the tubers 



tubers which 



were cut in half transversely, those buds near the exposed sur- 

 face starting first. Subdued light and a treatment consisting of 

 wrapping the potatoes with cotton saturated with hydrogen 

 peroxide were both effective in shortening the rest period in 

 new tubers with skins not highly suberized. The author believed 

 the shortening of the rest period in all these cases to be correlated, 

 not with water absorption, but with increased absorption of 



oxygen. 



In his studies of the rest period of plants, Howard ('15) found 

 that when certain agents, such as etherization, desiccation, warm 

 water bath, etc., were used to break the rest period, the diastatic 

 activity of the treated tissues was increased, such increase 

 agreeing in each case with the extent to which the treatment 

 broke the rest period. Corresponding with this increased dia- 

 stase activity, the amounts of soluble reducing sugars were also 

 found to increase within 24 hours after application of the treat- 

 ment, provided the treatment was applied during the early 

 winter. Treatments given later in the season were found to 



have very little effect. 



The work of Howard is confirmed to some extent by that of 

 Bonns ('18) in this laboratory. The latter, in studying the effect 

 of etherization upon enzyme activity in corms of Gladiolus, 



