Igtt] _ APPLEMAN—AFTER-RIPENING OF POTATO 313 
Potatoes stored at o° C. or below exude an acid fluid. This 
fact suggested the possibility that the increased diastatic activity 
after cold storage may be due to free acids. The decreased cata- 
lase activity might also be thus accounted for. The following 
single experiment is evidence in favor of this view. 
Two potatoes of nearly equal weight were grated and thor- 
oughly ground, one with CaCO,, and the other without. Both 
were stored at o° C. for 34 days, and analysis made according to 
table VII. 
TABLE VII 
EFFECT OF STORAGE AT 0° C. FoR 34 DAYS WHEN POTATO IS PREVIOUSLY GROUND 
WITH AND WITHOUT CaCO, 
. GLucosE - DIASTASE PEROXIDASE CATALASE 
Porta BS ; : 
eg ti a Units of extract |Seconds required ne Gh, evelued 
Per cent to digest a to reach in 5 min. 
unit of starch | standard color 
et CAO eae 100 30 o.1 
MRO trace 160 40 7 
_ The expressed potato sap is strongly acid. After repeated 
titrations, I found that the sap from cold storage potatoes and 
that from room-stored ones contained practically the same amount 
of acid. Low temperature, therefore, does not change the total 
acidity, but probably affects the permeability of protoplasmic 
membranes, and thereby allows the acids to reach zymogens more 
rapidly than under normal conditions. — 
Conclusion and summary 
The method recommended by Griss for determining the rate 
of peroxidase activity in the potato tuber gives no indication of 
the rate of activity in conditions approaching those of the living 
tuber. This is due to errors introduced by inclusion of the peroxi- 
dase in the clot of coagulable proteins, and to the loss of peroxidase 
during the process of drying the slices. After a few days the 
peroxidase is practically destroyed in the dry powdered potato. 
This method always showed an apparent increase in peroxidase 
activity in cold storage potatoes. The evidence at hand seems to 
indicate that this is due to an alteration of coagulable proteins 
