622 
ME. J. BROUGHTON ON A CERTAIN EXCRETION OE 
plants, when placed in circumstances where access of oxygen is no longer possible, con- 
tinue to give off carbonic acid, in quantities and under conditions which involve the 
conclusion that it is a necessary function of the life or growth of the plant. 
There appear to be but two ways of accounting for this excretion of carbonic acid : — 
1st. It may possibly be due to absorption of oxygen occurring long prior to the exha- 
lation. 2nd. It may be due to the direct giving off of carbonic acid in consequence of 
the chemical changes occurring in the plant. It may also be a consequence of both 
conjointly. 
If it were possible to exclude oxygen from a plant during the whole of its life, or if 
a plant could be grown for some months in a mixture of neutral gas and carbonic acid, 
the exhalation of the latter gas must necessarily be ascribed to the second hypothesis. 
Experiments in this direction, however, offer extreme difficulties, or are even impossible. 
De Saussure states that no plants will live in an atmosphere destitute of oxygen. 
There is, however, a doubt whether this conclusion is perfectly general. 
There is, however, another plan by which considerable light may be obtained in the 
matter. It consists in ascertaining the quantitative effect produced on the exhalation 
of carbonic acid from parts of plants by their exposure to the oxygen of the air during 
periods of known direction. This I have endeavoured to carry out as follows. 
A certain weight (usually 5 grms.) of leaves or bark was exposed to air for twenty-four 
hours in a bell-jar over water immediately after being separated from the plant. In the 
case of bark it was found necessary to do this while still attached to the wood. An equal 
amount, as similar in character as possible, was exposed for the same period to an atmo- 
sphere of nitrogen. Thus the two cases only differed by a day’s exposure to the influence 
of oxygen. The effect of this was ascertained by placing each in a eudiometer over mer- 
cury, and measuring the respective amounts of carbonic acid given off each day. 
The following Tables express the results obtained. The first column gives the number 
of days after the separation from the plant. Column marked “ Air ” relates to the spe- 
cimen exposed to air, that marked N refers to the one placed in nitrogen. The column 
A expresses the difference of the two, or the effect of a day’s exposure. The results are 
given in cub. centims. of dry C0 2 reduced to the ordinary standard. 
Bark of Litscea oblonga. 
Bark of Cupressus Lusitanica. 
Bark of Acacia dealbata. 
I. 
Air. 
N. 
A. 
I. 
Air. 
N. 
A. 
I. 
Air. 
N. 
A. 
2 
6-20 
5*50 
0-70 
2 
2-06 
1-53 
0-53 
2 
5-14 
409 
1-05 
3 
6-13 
4-37 
1-86 
3 
2-54 
2-05 
0-49 
3 
3*85 
3-04 
0-81 
4 
5-06 
410 
0*96 
4 
2-20 
1-91 
0-29 
4 
4-37 
4-30 
0-07 
5 
4 - 39 . 
3-76 
0-63 
5 
2-10 
1-94 
0-16 
5 
2-61 
2-60 
0-01 
6 
4-26 
3-70 
0-56 
6 
1’65 
1*65 
0-00 
6 
2-10 
2*10 
0-00 
7 
3-39 
3-35 
0-04 
7 
1-49 
1-49 
0-00 
7 
1-61 
1-61 
0-00 
| 8 
2-89 
2-89 
0-00 
8 
1-20 
1-20 
0-00 
I 9 
2-38 
2-38 
0-00 
9 
1-05 
j 1*05 
! o-oo 
: io 
l -'62 
1-64 
- 0-02 
; ii 
1-74 
1-74 
0-00 
12 
1-72 
1-72 
0-00 
! 13 
1 
0-85 
0-85 
0-00 
