1919] 



MCGINTY — DIASTASE ACTIVITY OF SOLANUM TUBEROSUM 231 



Some other facts also introduced an element of doubt into the 

 matter. Beets and mangels, which store their carbohydrates as 

 sugar instead of starch, were found to possess highly diastatic 

 leaves, while the roots contained none of the enzyme. No trace 

 of starch could be found in roots of the radish, yet it was one of 

 the most diastatically active tissues studied. Likewise the 

 potato tuber, which is, of course, particularly rich in starch, 

 proved to be poor in diastase. The leaves of different species 

 of plants were found by them to vary greatly in diastase content. 

 The enzyme appeared most abundant in leaves where, to quote 

 them, " starch is never stored permanently, but where it may be 

 found in small amounts during photosynthesis." These state- 

 ments do not agree very well with that made by Haas and Hill 

 ('17, p. 369), which is as follows: "The amount of diastase is 

 always greater in starch leaves than in sugar leaves, and the same 

 holds for insolated leaves containing much starch, as compared 

 with shaded leaves containing little or no starch." 



In studying this problem of carbohydrate synthesis in plants, 

 Bradley and Kellersberger made some determinations of dia- 

 static activity which are of interest in connection with the pres- 

 ent problem, and a few of these are given below. The figures 

 have been recalculated on the basis of 100 which represents 

 the greatest activity reported. 



Relative diastatic Amount of 



Plant activity starch content 



Pea, seeds, medium 100.0 Medium 



Pea, seeds, mature 50.0 Abundant 



Corn, seeds, young 10.0 Medium 



Corn, seeds, medium 6.7 Abundant 



Corn, seeds, mature 7.7 Abundant 



Corn, cob, young 7.7 Small 



Corn, cob, mature 7.7 Small 



Corn, husk, young 25.0 None 



Corn, husk, mature 8.3 None 



Potato, root, medium 2.8 Some dextrin 



Potato, tuber, medium 2.9 Very abundant 



Potato, leaf, medium 75.0 None 



* Potato leaves generally contain starch, but in this case they were obtained in 

 the early morning before photosynthesis had taken place to any extent. 



* 



