AND OF PLANTS UPON THE ATMOSPHERE. 
165 
The proportion of carbonic acid in the jar was each morning made equivalent to 5 or 
6 per cent, by additions through the tube. 
The first day no great alteration in the air was detected, but on the second day, by 
eight in the evening, the oxygen had risen to 26*5 per cent. In the morning it had 
sunk to 26, but by 2 p.m. it had again risen to no less than 29‘/5, and by sunset it 
had reached 30 per cent. At night it sunk one half per cent. ; but the effect during 
the following day was not estimated, as the sickly appearance which the plant now 
began to assume induced me to suspend the experiment. 
In a second trial, however, the branch of a healthy Lilac growing in the garden was 
introduced into the same jar, where it was suffered to remain until its leaves became 
entirely withered. 
The first day the increase of oxygen in the jar was no more than 0-25 per cent., but 
on the second it rose to 25'0. At night it sunk to nearly 22 per cent., but the next 
evening it had again risen to 2 7 per cent. This was the maximum of its increase, 
for at night it sunk to 26, and in the morning exhibited signs of incipient decay. 
Accordingly in the evening the oxygen amounted only to 265 ; the next evening to 
255 ; the following one to 24‘75 ; and the one next succeeding it had sunk to the 
point at which it stood at the commencement, or to 21 per cent. 
The reason of this decrease was, however, very manifest in the decay and falling 
off of the leaves ; so that this circumstance does not invalidate the conclusion which 
the preceding experiments concur in establishing, namely, that in fine weather, at 
least so long as the plant continues healthy, it adds considerably to the oxygen of 
the air when carbonic acid is freely supplied. 
In the last instance quoted, the exposed surface of all the leaves inclosed in the 
jar, which were about fifty in number, was calculated at no more than three hundred 
square inches, and yet there must have been added to the air of the jar as much as 
twenty-six cubic inches of oxygen, in consequence of the action of this quantity upon 
the carbonic acid introduced. 
But there is reason to believe, that even under the circumstances above stated 
(which were more favourable to the due performance of the functions of the plant 
than those to which Mr. Ellis’s were subjected,) the amount of oxygen evolved was 
much smaller than it would have been in the open air, for by introducing several 
plants into the same jar of air in pretty quick succession, I have succeeded in raising 
the amount of oxygen contained from 21 to 39 per cent., and probably had not even 
then attained the limit to which the increase of this constituent might have been 
brought. 
How great then must be the effect of an entire tree in the open air under favour- 
able circumstances ! and we must recollect that, cceteris paribus, the circumstances 
will be favourable to the exertion of the vital energies of the plant, within certain 
limits at least, in proportion as animal respiration and animal putrefaction furnish to 
it a supply of carbonic acid. 
