RESPIRATION IN PLANTS 
225 
activity rather than oxidases and catalase. This paper, however, is 
not concerned with the chemical nature or mode of action of these 
substances, nor is it concerned with any particular theory of respira- 
tion. Therefore, an exhaustive citation of the literature is not perti- 
nent to the matter in hand. The sole object in view was a quantita- 
tive study of the relation of both oxidase and catalase activity to 
intensity of respiration. Potato tubers seemed especially favorable 
material for a study of this kind, since respiration in these tubers is 
greatly accelerated by various artificial treatments and is subject to 
fiuctations under natural conditions, as greening, sprouting, etc. The 
rate of respiration also varies in different parts of the same tuber 
and tubers of different varieties. Besides, these tubers contain very 
active oxidases and catalase. The modification of the intensity of 
respiration in the tubers was determined and at the same time measure- 
ments were made of both the oxidase and catalase activity in the 
juice. 
Methods 
Respiration: The rate of respiration was determined by the 
amount of CO2 expired from the tubers. No attempt was made to 
control the temperature, but all measurements that are compared 
were made at the same time and under identical conditions. Tubers 
of about a kilo's weight were allowed to respire twenty-four hours for 
each determination. 
Oxidase: A manometric method was used for the oxidase deter- 
minations, the oxygen absorbed during the reaction being measured 
by the change of pressure within Bunzel's simplified apparatus. 
Both pyrocatechin and hydrochinon were first employed as the oxidiz- 
able substance, but it was soon found that they showed the same 
general relations in respect to oxidase activity under different condi- 
tions. Since the reaction with hydrochinon was very slow as com- 
pared with that of pyrocatechin, its use was soon abandoned in favor 
of pyrocatechin as the sole reagent. From Bunzel's^ work on the 
"Oxidases in Healthy and in Curly-Dwarf Potatoes" in which he 
used 18 ring compounds, it may be concluded that the use of one 
favorable compound of this nature would give just as valuable com- 
parative results as use of a larger number. He found a wide variation 
in the amount of oxygen absorbed by the different compounds, 
but aside from one or two exceptions, they all showed the same general 
