acid gas, and the globules of air rose from the 
denuded parenchyma ; and it is shewn both from 
the experiments of Sennebier and Woodhouse, 
that the leaves most abundant in parenchymatous 
parts produce most oxygene in water impregnated 
with carbonic acid. 
Some few plants * will vegetate in an artificial 
atmosphere, consisting principally of carbonic acid, 
and many will grow for some time in air, contain- 
ing from one-half to one-third ; but they are not so 
healthy as when supplied with smaller quantities of 
this elastic substance. 
Plants exposed to light have been found to pro- 
duce oxygene gas in an elastic medium and in 
water, containing no carbonic acid gas; but in 
quantities much smaller than when carbonic acid 
gas was present. 
In the dark, no oxygene gas is produced by 
plants, whatever be the elastic medium to which 
they are exposed ; and no carbonic acid absorbed. 
In most cases, on the contrary, oxygene gas, if it 
be present, is absorbed, and carbonic acid gas is 
produced. 
In the changes that take place in the com- 
position of the organized parts, it is probable that 
saccharine compounds are principally formed 
during the absence of light ; gum, woody fibre, oils, 
and resins, during its presence ; and the evolution 
of carbonic acid gas, or its formation during the 
night, may be necessary to give greater solubility to 
* I found the Arenaria tenuifolia to produce oxygene in car- 
bonic acid, which was nearly pure. 
