1900] BRIEFER ARTICLES 441 
collect in the tube or against the top of the beaker, as the larger ones 
do, or remain clinging to the leaves; or if only they displace water, 
they may stay within the tissues of the plant, and still make their record, 
Of course having a rod whose upward movement shows the rapidity 
of the evolution of oxygen, it can very easily be made to leave its 
record ; most accurately perhaps by means of the wheel described as 
the chief part of a “a new self-registering transpiration machine, ’’? 
but more conveniently sometimes, being less disturbed by drafts, by 
means of a lever auxanometer. One illustration shows it set up with a 
Corbett auxanometer (jig. 2); the other, with the wheel (fg. 3). 
From a considerable bulk of green plant substance the evolution of 
oxygen is so rapid that it is necessary to use a rather large rod or get 
an inconveniently rapid drop of the tracer. With the auxanometer 
it is better to have the arms of the lever equally long. And with the 
wheel the tracer may be attached directly to the counterpoise, thus 
using only one wheel. I have tried the apparatus with Elodea and 
with Callitriche. The short record given here as an illustration of 
its work was obtained with Callitriche, May 10, beginning at 11:20 
A.M., after a freezing night. The experiment was performed on the 
the roof, so that there were no shadows except from occasional clouds. 
The distance descended by the tracer and the indicated evolution of 
oxygen are both given. A change in weight of 1%, by the evolution of 
1 of oxygen, caused the tracer to fall 17.7™". The registration was 
on a cylinder revolving in 20 minutes, but for the sake of brevity the 
record is condensed into one hour intervals. ‘The temperature at 11 
A. M. was 19°C.; at 1 P. M., 23°; and at 7 P. M., 21°. 
II:20-12 12-1 2 3 3-4 4-5 5-6 6-7 6: 40-7 
mm. 6.8 14.8 28.7 32.2 37.8 31.8 21.0 11.2 1.7 
me 0.37 «O84. 1.63 | 2.82 2.ig  1B0 Ey 5 0.63 - 6.006 
With the same plants on another day it was found that at 31° the 
evolution of oxygen was above 3” per hr., while at 36.4° it was only 
about 1° in the same interval. The explanation must be sought 
largely in the decrease in available CO, at the higher temperature.— 
DWIN B. CopeLanp, University of West Virginia, Morgantown. 
* Bor. Gaz. 26:343. 1898. 
