THE LADIES MAGAZINE OF GARDENING. 
333 
vessels, and conducted alternately in sunshine and in shade, by careful 
and exact analyses of the air in its different conditions, and by accurate 
measurements of its quantities at different periods of the experiment, has 
removed many apparent anomalies, and opened the way, as we think, to 
a consistent and satisfactory view of the subject. 
In his experiments before referred to, and published in the Annales de 
Chimie , 1797, this distinguished Chemist found that when garden peas 
( P\sum sativum ), which had attained to the height of between three and 
four inches, were placed in a recipient of atmospheric air, inverted in a 
saucer filled with water, and then set aside in a room well lighted, but 
which did not receive the direct rays of the sun, they grew well. At the 
end of ten days the volume of air was considerably diminished, its purity 
greatly impaired, and it still retained -j-J-o of carbonic acid. Plants of 
Mentha aquatica effected similar changes in the air, whilst they continued 
to grow in the shade; whence it is inferred that plants, like animals, con¬ 
tinually deteriorate the air, by converting its oxygen into carbonic acid 
gas, when they vegetate in the shade; a result confirmed by many experi¬ 
ments long since made by the author, and given to the public in the years 
1807 and 1811. 
In prosecuting his experiments on vegetation under the direct influence 
of light, M. De Saussure was led, with others, to the conclusion, that, if 
the air which may have been deteriorated by the growth of plants in the 
shade, be exposed for a short time to the sun s rays, it recovers its former 
purity. In his Recherches Chimiques sur la Vegetation , published in 
1804, he has established this position by numerous experiments on various 
plants, as Mentha aquatica , Lythrum Salicaria , Pinus sylvestris genevensis , 
and Cactus opuntia. These plants were confined in glass vessels of 
atmospheric air, and kept for eighteen or twenty hours in the shade, or 
in perfect darkness; but early in the morning the vessels were taken out 
and exposed for four or five hours to a bright sunshine; after such 
exposure, the air was examined, and was then found to have suffered no 
change whatever, either in purity or in volume. 
By other experiments, the author next proceeds to show that, though 
the air when thus exposed to light had recovered its original composition, 
it must, during the experiments, have undergone successive changes of 
deterioration and renewal. If a substance, as moistened quicklime, which 
strongly attracts carbonic acid, were placed in the vessel with the growing- 
plants, the volume of air was observed to diminish, even although the 
apparatus were placed in sunshine; the air, too, when analysed on the 
fifth or sixth day of the experiment, afforded only or had lost five per 
cent, of oxygen gas ; whilst similar plants confined in another vessel, but 
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