20 THE VITAL FUNCTIONS. 



deed, but they were exceedingly stinted in their growth, and 

 evidently derived little or no sustenance from the water with 

 which they were supplied. Experiments of a similar nature 

 were made hy Bonnet, and with the like result. When plants 

 are contained in closed vessels, and regularly supplied with 

 water, but denied all access to carbonic acid gas, they are 

 developed only to -a very limited extent, determined by the 

 store of nutritious matter which had been already collected in. 

 each plant when the experiment commenced, and which, by 

 combining with the water, may have afforded a temporary 

 supply of nourishment. 



But the water which nature furnishes to the vegetable or- 

 gans is never perfectly pure; for, besides containing air, in 

 which there is constantly a certain proportion of carbonic 

 acid gas, it has always acquired by percolation through the 

 soil various earthy and saline particles, together with mate- 

 rials derived from decayed vegetable or animal remains. 

 Most of these substances are soluble, in however minute a 

 quantity, in water: and others, finely pulverized, may be 

 suspended in that fluid, and carried along with it into the 

 vegetable system. It does not appear, however, that pure 

 carbon is ever admitted; for Sir H. Davy, on mixing char- 

 coal, ground to an impalpable powder, with the water into 

 which the roots of mint were immersed, could not discover 

 that the smallest quantity of that substance had been, in any 

 case, absorbed.* But in the form of carbonic acid, this ele- 

 ment is received in great abundance, through the medium of 

 water, which readily absorbs it: and a considerable quantity 

 of carbon is also introduced into the fluids of the plant, de- 

 rived from the decomposed animal and vegetable materials, 

 which the water generally contains. The peculiar fertility 

 of each kind of soil depends principally on the quantity of 

 these organic products it contains in a state capable of being 

 absorbed by the plant, and of contributing to its nourish- 

 ment. 



* Elements of Agricultural Chemistry, Lcct. VI. p. 234. 



