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nally contained : water, therefore, cannot be considered as the sole 

 food of plants. 



If water does not constitute, alone, the food of plants, it is, how- 

 ever, absolutely necessary to their existence ; serving as the vehicle, 

 by which those substances, from which they derive a larger portion 

 of nutriment, are conveyed through their system of vessels. Water 

 is also, most probably, so acted on in the vegetable system, that it 

 is resolved into its two simple principles, hydrogen and oxygen: 

 both of which are well known to exist, in almost every vegetable 

 substance ; and are presumed to be absolutely necessary to the 

 performance of various important functions, in the vegetable 

 oeconomy. 



In all vegetables is discovered, by analysis, a considerable por- 

 tion of carbon ; particularly in those, in which the woody fibre is 

 most abundant : thus, in trees, it constitutes, upon an average, 

 nearly a fifth of their whole substance. Analysis has also mani- 

 fested, that the water which drains from a dung-hill, and all fertile 

 soils, contain a very large proportion of carbonaceous matter. That 

 carbon, therefore, is a food of plants, appears to be established 

 almost beyond a doubt. 



How indispensible to vegetation are the various combinations of 

 earths, must be evident to every one. They form a proper medium, 

 by which the due quantity of water is regularly diffused, and ad- 

 ministered, to the various plants which the ground bears. They 

 also form a mass sufficiently yielding to allow the ready extensions 

 of the roots of plants, in every direction ; at the same time pos- 

 sessing sufficient tenacity and firmness, to secure them stability 

 in their situation. 



But chemical analysis has demonstrated, that all* plants contain 

 more or less of earth in their composition. Saussure, jun. planted se- 

 veral trees in a granitic, and in a calcareous soil : and after analysing 

 the soil, analysed the trees ; when he found, that the trees which 



