Physiologie. 165 



Certain internal changes are accelerated by 0°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 six 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 zy mögen by free acids, which 

 are liberated by the greater permeability of protoplasmic membra- 

 nes at low temperatures. 



Catalase is very abundant in potato tubers stored either at C C. 

 or at room temperature, but suffers a gradual reduction as storage 

 at 0° 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 iricreases slowly as the end of 

 the rest period approaches. Low temperature had no appreciable 

 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 casual 

 relation to these processes. Moore. 



Bunzel, H. H., The measurement of the oxidase content 

 of plant juices. (U. S. Dept. Agric. Bur. of PI. Ind. CCXXXVIII. 

 p. 1—40. p. 1-2. fig. 1-9. March 9, 1912.) 



A new method for the estimation of oxidases in plant juices 

 based upon determining the quantities of oxygen absorbed by 

 measuring the changes of pressure within the reaction flask, is 

 described. The apparatus consisting of a thermostat (for which the 

 temperature regulator, fans for air agitation, heater, cooling devices, 

 etc., are especially adapted) shaking, oxidase titration and other 

 parts is discussed in detail. 



Experiments conducted with the described apparatus, using 

 potato juice, resulted in the following conclusions: 1. Only a very 

 definite and limited quantity of oxygen is absorbed by pyrogallol 

 in the presence of a definite quantity of potato juice within a period 

 of two or three hours. 2. The concentration and total quantity of 

 pyrogallol present is without effect on the final result, provided the 

 pyrogallol is in excess. 3. The oxidase in potato juice which accele- 

 rates the oxidation of pyrogallol by atmospheric oxygen, is not an 

 enzyme in the customary sense of the word, but rather a substance 

 entering directly into the reaction and being destroyed in the course 

 of the same. 



A unit of Standard for expressing the strength of a juice is 

 proposed as follows: an oxidase Solution of such strength that 1 

 litre of it will be capable of bringing about the consumption of 



