1919] 



MCGINTY — DIASTASE ACTIVITY OF SOLANUM TUBEROSUM 



243 



fourth column. The latter is expressed in terms of 100, which 

 is assumed to be the value of the greatest activity observed. 



table I 



DIASTASE ACTIVITY IN RELATION TO STAGE OF DEVELOPMENT OF 



POTATO TUBERS* 



Stage of 



development 



(diameter 



in cms.) 



N 



No. cc. — KMn0 4 used in titrating Cu 2 



20 



Juice + starch 

 (incubated) 



Juice + water Juice + water 



Relative 

 diastatic 



• • 



activity 



(incubated) 



(boiled) 



1 



2 



3 



4 



5 

 6 



Seed potato 

 Seed potato 

 Seed potato 



10.7 



13.0 



12.8 



9.9 



6.2 



5.7 



Lost 



11.4 



10.0 



7.1 



3.5 



2.9 



11.0 

 8.2 



9.6 



8.4 

 6.6 

 7.3 



8.0 

 10.1 

 8.7 

 6.5 

 2.2 

 1.7 



7.8 

 6.5 

 7.1 



66 

 71 

 100 

 83 

 98 

 98 



78 

 41 

 61 



* In the growing potatoes, not less than 500 gms. of the tubers were used, in each 

 case, as the source of the juice. 



It appears from these figures that advance in stage of develop- 

 ment is accompanied by an increase in diastatic activity. The 

 author is inclined to believe that the high value obtained for 

 tubers 3 cm. in diameter is perhaps abnormal and without 

 particular significance. 



The diastatic activity of three samples of seed potatoes is also 

 given for purposes of comparison. The first two were taken 

 from the lot that was used for seed, while the third represents a 

 different variety. They had been kept in ordinary storage up 

 to the time the analyses were made. It will be observed that 

 their diastatic activity is considerably lower than that of most 

 of the growing tubers. It is rather surprising that the two 

 samples from the same lot of stored tubers should possess such 

 widely different diastatic activities as 78 and 41. 



The second column in table i is included to show the increase 

 in reducing sugars which occurs when the juice alone (diluted 



