93 
331. Many experiments of M. de Saussure seem, 
likewise, to prove that air exists naturally in plants. 
He found that green-leaved plants, especially such as 
had fleshy leaves, lived a long time in pure nitrogen, 
and afforded to it a considerable portion of oxygen 
gas in the sun, but yielded only carbonic acid in the 
shade. Similar results were obtained when the 
plants were confined in an atmosphere of the gase- 
ous oxide of carbon. Many fleshy plants continued,, 
also, to vegetate in vacua, which M. de Saussure sup- 
posed them capable of doing only in consequence of 
the air they contained in their parenchymatous struc- 
ture, which air was decomposed and eliminated by 
the action of the sun *.' If, farther, we believe that 
the decomposition of carbonic acid by leaves is ef- 
fected only in their parenchymatous structure, we 
must necessarily suppose, that, in the experiments of 
Davy and De Saussure, as well. as in all others in 
which this gas was decomposed, it must first have en- 
tered into the substance of the leaf. From the facts, 
therefore, which have now been stated, it seems to 
follow that gaseous fluids obtain admission into plants, 
both through the medium of solution in water, and 
under an elastic form. 
332 But the carbonic acid, which may thus enter 
vegetables, we have seen to undergo decomposition 
(S ; 7.)- and to be partly expelled in the state of oxygen 
gas How far, then, are we entitled to consider these 
operations as the necessary result of a living vegetable 
function? Preparatory to the decision of this question, 
* Rechcrcues, p. 200. 9, 14. 
