COMPARATIVE STUDIES ON RESPIRATION XVIII. 
RESPIRATION AND ANTAGONISM IN ELODEA 
C. J. Lyon 
(Received for publication March 19, 192 1) 
Previous studies in this series have dealt with the relation between 
antagonism and respiration, but have not included tissues of higher plants 
containing normal amounts of chlorophyll.^ The experiments here pre- 
sented were designed to test the effects of mixtures of solutions of sodium 
and calcium chlorides on such tissues. 
For this purpose the leafy stems of Elodea canadensis were selected. 
This has proven to be excellent material since it is hardy in respect to 
climatic conditions and laboratory manipulation while sufficiently sensitive 
to reagents. The leaves are exceedingly thin, and gaseous exchange is 
very rapid. 
All the plants were collected from one place in a slowly flowing stream 
and, as long as it remained open, taken fresh at least once a week to the 
laboratory. The material used during the late winter and early spring was 
provided by a quantity of plants collected in December and kept in the 
greenhouse in large glass jars in a cool room. It thrived well and when 
tested gave normal results. 
The method used for most of the experiments was that developed by 
Haas^ in which the plants were immersed in solutions containing an indi- 
cator.^ The production of CO2 was measured by the change in color of 
the indicator. The standard buffer solutions containing the same indicator 
were mixtures of borax and boric acid. 
The final experiments were carried out by the use of the apparatus 
described by Osterhout.^ The curves closely resemble those obtained b}^ 
the other method. The accuracy of measurement was greater. Since the 
two methods are alike in all but mechanical details, only the first will be 
discussed in full. 
The procedure consisted in measuring the normal rate of production 
of CO2 in tap water or distilled water and then testing the efTect of a salt 
1 The experiments on wheat reported in a previous paper of this series were made upon 
germinating seeds which contained Httle or no chlorophyll. Cf. Thomas, H. S. Jour. Gen. 
Physiol, i: 203. 1918. 
2 Haas, A. R. C. Science N. S. 44: 105. 1916. 
3 The plants were thoroughly washed to remove any adhering organisms. Micro- 
scopical inspection showed that the plants used for the experiments were almost free from 
bacteria. 
^ Osterhout, W. J. V. Jour. Gen. Physiol, i: 17-22. 1918. 
