310 BOTANICAL GAZETTE [OCTOBER | 
It is not due to activation of zymogen, as the phenomenon does not 
occur in the fresh unheated extract method described later. 
TABLE II 
SHOWS INCREASE IN PEROXIDASE ACTIVITY OF SOLUTION ON STANDING 
SECONDS REQUIRED FOR REACTION TO REACH 
STANDARD TUBE 
| After 2 hours | After 24 hours 
Slices of potato dehydrated with alco- 
hol and ether; heated to 70° C. for 
CPU so ee tae 51 34 3° 
A third source of error, which would have to be taken into 
account, is the degree and time of drying. If the slices are dried 
in a desiccator for several hours, the peroxidase activity is greatly 
impaired. After a few days the peroxidase is practically destroyed 
in the powder produced by grinding the dried slices (table II). 
Gortner (6) has recently described a tyrosinase, which loses its 
vitality on drying. 
TABLE III 
SHOWS LOSS OF PEROXIDASE IN POTATO WITH DRYING 
| Time required for re- 
| action to reach blue 
Potato tuber | 
. of standard tube 
| 
} 
24 seconds 
Slices dried in desiccator 30 min................| 
i 120 seconds 
Slices dried in desiccator 22 hrs...............-. 
Powdered slices standing 4 days exposed to labora- 
ory air 
ro minutes 
The above facts alone are sufficient to render the method 
described by Griiss of little value for determining peroxidase 
activity in conditions approaching those of the living tuber. By 
grinding the potato tuber with CaCO,, thus neutralizing the acids, 
the peroxidase activity was found to be quite stable for some 
time in the resulting extract (table IV). 
Based upon this fact the following procedure was employed 
for the final comparative determinations of the peroxidase in the 
potato tubers under investigation. The tubers were grated with 
frequent dipping of the surface in CaCO,. The pulp was then 
