314 BOTANICAL GAZETTE [OCTOBER 
by low temperature, thus modifying the amount of peroxidase 
occluded by the clot. 
Certain internal changes are accelerated by o° C., which shorten 
the rest period of potato tubers. 
Both glucose and sucrose accumulate. © The increase in sucrose 
is more rapid at first than glucose, but by the end of 6 weeks of 
storage at low temperature the percentage of glucose is about 
twice that of sucrose. 
Diastase activity was greater in the cold storage tubers than 
in those stored at room temperature at the end of 2 and 4 weeks; 
but at the end of 6 weeks there was no appreciable difference, 
as the variety used for this work was near the end of the rest 
period. A few had already germinated. The increased diastase 
activity is probably due to greater activation of zymogen by free 
acids, which are liberated by the greater permeability of proto- 
plasmic membranes at low temperatures. 
Catalase is very abundant.in potato tubers stored either at 
o° C. or at room temperature, but suffers a gradual reduction as 
storage at o° C. continues. The presence of free acids would cause 
this reduction, as catalase is rapidly destroyed by the free acids in 
ground potato pulp. This behavior of catalase corresponds with 
that of respiration under similar conditions, a significant fact in 
the light of a recent claim (3) that catalase is the primary factor 
in alcoholic fermentation, and therefore probably in respiration. 
A guaiaconic acid peroxidase is very active in potato tubers at 
the beginning of the rest period and increases slowly as the end 
of the rest period approaches. Low temperature had no appre- 
ciable effect in hastening this increase in the material used for this 
work, according to the method employed for its determination. 
The changes peculiar to after-ripening may be in the buds, and 
the metabolism of the tuber as a whole may bear little or no causal 
relation to these processes. 
The writer wishes to acknowledge his indebtedness to Dr. 
Wi11am Crocker for suggesting the problem and for his untiring 
interest and assistance during the progress of the work. 
AGRICULTURAL EXPERIMENT STATION 
CoLLecE Park, MARYLAND 
