Wounded Plants. 
533 
in the U-tubes for washing the air from C0 2 was frequently 
renewed ; that care was taken that the air supplied to the 
plants in the receiver should be sufficiently moist, and so 
forth. All the manipulations of the experiments and 
analyses were carried on each time in as nearly a similar 
manner as possible to ensure equality in the results. For 
the analyses the same burette and pipettes were used through- 
out the whole course of the work. The titrations were made 
with a solution of hydrochloric acid of such a strength that i cc. 
equalled i mg. of C0 2 , and for an indicator phenol-phthalein 
was employed. 
The constant flow of air or gas through the apparatus was 
obtained by means of a Stainer’s drop-aspirator regulated 
with a gas-meter (Experimentir-Gas-Messer of Elster), by 
which means no difficulty was found in keeping the current 
within 50 cc. per hour of the amount desired. The rapidity 
of the current was nearly 3*5 litres per hour, an amount to 
which the apparatus held with surprising constancy throughout 
the time it was used. When gases other than air were run 
through the apparatus, it was necessary to be somewhat 
careful to regulate the pressure from the gasometer so as 
to avoid an increase in the gas-stream. Even in such cases, 
however, no difficulty was found in keeping the flow at the 
desired rate. The hydrogen and oxygen used were first 
washed roughly at the time of preparation with KMn0 4 and 
KOH, and again, when being used, by means of U-tubes con- 
taining KMn0 4 , KOH, and HgCl 2 interpolated between the 
gasometer and the receiver containing the plants. 
In every case the receiver containing the plants was im- 
mersed in a large vessel of water, and thereby kept at an 
approximately constant temperature, which usually varied but 
little more than half a degree during the day, the average 
temperature being about 20 - 5 °. 
For the determination of the relative amounts of C0 2 pro- 
duced and of 0 2 absorbed, or, as it is usually expressed, the 
equation 
C0 2 
0 2 
, a form of apparatus somewhat different from 
