334 
THE LADIES’ MAGAZINE OF GARDENING. 
without lime, produced no change, either in the purity or volume of their 
atmosphere. Now, the diminution of volume in the experiment with 
lime shows that there had been an attraction, and consequently a form¬ 
ation of carbonic acid gas ; for the lime which produced the diminution 
acted only on that gas. The experiment, it is added, shows farther, that 
the formation of carbonic acid gas is necessary to vegetation, even in 
sunshine, and that the reason why we do not perceive its production by 
the plants which vegetate without lime in common air, is because they 
then decompose it in proportion as they form it with the surrounding 
oxygen. (Kecherches Chim ., p. 35, 36). 
This inference, respecting the simultaneous formation and decomposition 
of carbonic acid, derived from experiments made with common air, is 
supported by others, in which an artificial atmosphere, containing about 
seven per cent, of carbonic acid, was employed. Plants of the same species 
as those before mentioned were made use of; the same periods of alternate 
exposure in the shade and in sunshine were observed; and the same times 
allotted for the duration of the experiments. The total volume of air, at 
the end of the experiments, had undergone little variation, but its compo¬ 
sition was greatly changed. The carbonic acid gas which was added to 
the atmosphere had more or less completely disappeared, and its place was 
supplied by an increase of oxygen gas, so as to raise its proportion from 
twenty-one to twenty-four or twenty-six per cent. In these experiments, 
therefore, not only was the carbonic acid naturally formed by the vege¬ 
tation of the plants decomposed, but the excess of that gas which was 
added to the atmosphere underwent the same change; and the proportion 
of oxygen gas was consequently increased by five or six per cent, beyond 
that which occurred in the experiments with common air. 
From the results of these experiments, we learn that plants, like seeds, 
require the presence of oxygen gas in the atmosphere in which they grow, 
and, like them, also convert a portion of it into an equal volume of 
carbonic acid gas. This conversion is alike effected by their growth in 
the shade and sunshine. In the former case, however, the presence of 
this acid gas may be readily detected in the residual air by the usual 
tests ; but in the latter it escapes detection, because it is then decomposed 
as soon as formed, by the joint agency of the plants and solar light. 
Under a bright sunshine, therefore, the two processes by which carbonic 
acid is alternately formed and decomposed go on simultaneously; and 
their necessary operation, in as far as regards the condition of the air, is 
that of counteracting each other. Hence, though both may be continually 
exercised in favourable circumstances, the effects of neither on the atmo¬ 
sphere can be ascertained by ordinary means; and consequently, though 
