RESPIRATION IN PLANTS 
227 
oxid) in the short arm. The determinations were made in the same 
constant temperature box and shaken with the same shaker used for 
oxidase. The manometer reading at the end of five minutes constant 
shaking was considered the measure of catalase activity in .074 cc. 
of juice. All the catalase results, in the experimental part, represent 
the activity in this amount of juice, except when otherwise noted. 
The oxidase and catalase measurements were all made in duplicate 
and those whose results were not in close agreement were discarded. 
It was very desirable to use the same lot of juice for both catalase 
and oxidase measurements, but before this was possible it was neces- 
sary to determine what effect the CaCOs would have upon the oxidase 
activity. To this end, tubers were cut in half longitudinally so that 
each piece contained exactly one half of the seed and stem ends. 
One piece was grated without CaCOs and the other by dipping into 
CaCOs in the usual way for catalase determinations. Oxidase mea- 
surements were then made in the juice thus prepared. The average 
of seven determinations was exactly the same in both cases. There- 
fore, it is quite evident that the CaCOs exercises no appreciable effect 
upon the oxidase activity in potato juice, according to the method 
here employed for its measurement. 
The above conclusions regarding the effect on oxidase activity of 
CaCOs in the juice apply only with pyrocatechin. The effect may 
be otherwise with other chromogens. In fact, the presence of CaCOs 
in the juice seems to depress the oxidation of aloin, while the peroxidase 
activity is actually stimulated both in the case of aloin and guaiaconic 
acid. 
Experimental Results 
Ethyl Bromide: In a previous paper the writer'^ has shown that 
short exposures to ethyl bromide gas will about double the respiration 
in old McCormick potatoes. This treatment was repeated and 
catalase and oxidase determinations made on the same tubers used 
for respiration. Duplicate determinations on untreated tubers were 
made at the same time and under the same conditions. The results 
show that the treatment has no effect whatever on the oxidases. The 
catalase activity on the other hand is greatly increased in the treated 
tubers. 
