[Vol. 6 

 Z4U ANNALS OF THE MISSOURI BOTANICAL GARDEN 



of these for the same length of time and placing the other in 

 boiling water for 10 minutes to kill the enzyme. The diastase 

 activity determinations therefore included the following in 

 each case: one flask containing juice plus starch, incubated 

 12 hours; one flask containing juice plus water, incubated 12 

 hours; one flask containing juice plus water, boiled at once to 

 kill the enzyme. The cupric-reducing power of the solution in 

 the first flask less that of the solution in the third flask is con- 

 sidered to represent the activity of the enzyme. 



Some preliminary work seemed to indicate the presence of an 

 activating agent in the potato juice, in the absence of which the 

 enzyme possessed little or no activity. To determine this point, 

 some experiments were carried out according to the following 

 procedure: The enzyme, which was precipitated from about 

 200 cc. of potato juice by the addition of three volumes of 95 

 per cent alcohol, was collected on filter-paper and dried, and 

 then dissolved in 100 cc. of water and filtered, after which it 

 was ready for use. Another 200-cc. sample of the juice was 

 boiled, killing the enzyme and precipitating the proteins. This 

 was also filtered before using. 



In making the determinations, flasks were prepared as below. 

 The same amounts of diastase solution and boiled juice were 

 used in each instance, water being added to make the volume 

 the same in all cases. Two per cent of toluol was used as a 

 preservative. 



One flask containing starch plus enzyme. 



One flask containing starch plus enzyme plus boiled juice. 



These were incubated for varying periods of 12 to 24 hours 

 at 45° C. 



One flask containing enzyme plus boiled j uice. 



This was boiled at the beginning of the experiment to kill 

 the enzyme. 



After incubation the cupric-reducing powers of the solutions 



were determined and these accepted as an index of the diastatic 

 activity. 



Extraction of sugars. — For the sugar determinations, 50 gms. 

 of the green tubers (from the same lot used in the enzyme ac- 

 tivity determinations) were weighed out and immediately sliced 



