CABBONIC ACID BY LIVING PLANTS. 
619 
mass. Many kinds of leaves with which I have experimented appeared quite fresh and 
unchanged after fifteen days’ confinement in the eudiometer. 
When the investigation had arrived at this stage, it became necessary to consider the 
somewhat exceptional conditions under which the experiments were made. The plants 
grew and were experimented with on the Neilgherries at a height of 7400 feet, or 1-4 
mile up in the air. Hence the gases would meet with less mechanical impediments to 
their evolution than at the sea-level. To ascertain whether this circumstance had any 
essential effect on the phenomena, soda-water bottles were filled with leaves of Erica, 
fresh Cinchona bark, &c., and connected with manometer- 
tubes containing mercury (fig. 2). Soon the mercury began 
to rise, being pressed upwards by the gas exhaled, until 
the total pressure had become equal to 30 inches. Then 
it continued to rise several inches higher. In one case 
a final pressure exceeding a whole additional atmosphere 
was reached. The leaves were perfectly healthy, and 
showed no trace of any decomposition. In addition to 
these experiments others were made, in which the bottles 
filled with leaves &c. were fitted with delivery-tubes, whose 
ends were plunged a few inches below the surface of mer- 
cury. The gas was collected in a eudiometer. The results 
confirmed the other observations. This form of the experiment is well suited for a 
lecture illustration. Hence it is concluded that variations of atmospheric pressure 
within wide limits do not essentially affect this peculiar evolution of carbonic acid. 
All the foregoing experiments were performed with portions of plants separated from 
the root, and therefore under somewhat abnormal conditions. The important question 
arises, whether the same phenomenon constantly occurs in plants growing under ordinary 
conditions. Although there could be a priori little doubt of this, an experimental proof 
was desirable. It is one that offers many practical difficulties, and I have endeavoured 
to effect it as follows. 
I was first anxious to detect the exhalation of carbonic acid from growing Cinchona 
bark. As a preliminary qualitative experiment, I 
took a healthy young plant of C. officinalis , about 
two years old ; and by plucking off all the leaves from 
the stem, except those of the terminal shoot, it was 
enabled to be passed into a tube of glass, resembling 
the outer tube of a Liebig’s condenser (fig. 3), which 
was then made air-tight at each end by means of sheet 
caoutchouc and cement. The intervening space, be- 
tween the enclosed bark and the wall of the tube, 
was filled with hydrogen and allowed to remain 
for a day. It was then cleared out by a stream of 
hydrogen, and the upper branch tube conveying the hydrogen tied. The lower one had 
Pig. 3. 
