[Vol. 6 



236 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



One of the last-mentioned authors, Doby ('14), carried out 

 some experiments to determine the effect of the different sugars 

 upon the amylase of potatoes. From the results obtained, he 

 concluded that the action of the enzyme is inhibited by the 

 sugars in the following order, maltose being most effective, — 

 maltose, glucose, fructose, arabinose, galactose, mannose. 



He further concluded from his experiments that it is quite 

 probable that the action of amylase in a natural enzyme system 

 is restricted, in the first place by the decomposition products of 

 the substrate, and in the second place by other sugars which may 

 be present. 



Since maltose is the final product in the hydrolysis of starch 

 by amylase, it might seem that the activity of the enzyme would 

 soon be checked by the accumulation of this sugar, but Davis, 

 Daish, and Sawyer ('16), in their extensive work upon the for- 

 mation and translocation of carbohydrates in plants, found 



that maltose was immediately transformed into hexose by the 

 maltase present, so that there is only a trace of this sugar, in 

 leaves at least, at any one time. Moreover, Norris ('14) states, 

 as a result of experiments upon the factors influencing hydrolysis 

 of glycogen by diastase, that while the mixed products of hydrol- 

 ysis have a marked retarding influence on the velocity of the 

 reaction, maltose alone has very little effect. 



In studying the effect of activators upon the diastase of pota- 

 toes, Doby and Bodnar ('15) found, among other things, that 

 the boiled juice exerted a considerable activating influence. 

 Effront ('02) made a similar observation in regard to malt 



diastase. 



Carbohydrate transformations in the sweet-potato resemble to 

 a degree those in Solarium tuberosum. Hasselbring and Hawkins 

 ('15, '15a), and Hasselbring ('13), from their studies on this 

 subject, reached the conclusion that, while sweet-potatoes contain 

 only very small amounts of sugar during growth, the transforma- 

 tion of starch into sugar begins immediately after harvesting or 

 upon the killing of the vines by frost. The same changes were 

 found to occur whether the tubers were stored in cellars or 

 remained in the ground. These changes involved, according 

 to the authors, the transformation of starch to reducing sugars 



