82 Influence of the component Parts of the Soil on Vegetation, 



give reaeion to suspect that they must he coriside-red as com*, 

 pounds. 



&th, IVuter is the most general component part of soil, and 

 indeed, as a medium of solution, it keeps the nourishment 

 of plants in a fluid state, and promotes its circulation ; it is 

 decomposed in them into its principles hydrogen and oxygen, 

 and must therefore serve also as nourishment ; for the 

 oxygen is expired, and the hydrogen unites itself with the 

 solid parts. But however necessary water may be to vege- 

 tation, a superabundance of it has a prejudicial influence on 

 plants, as it softens their iibres, so that the oxygen can easily 

 produce a destructive putrefaction ; because they have na 

 longer suflicicnt elasticity to expire it. Hence the destruc- 

 tion of the crop by water in level fields, where marsh-plants 

 grow up in the room of the corn. 



■ Water lixiviates black mould in some cases, carries off the 

 extractible parts, and renders the ground poor. The in- 

 fluence of water on the sulphuric acid of cla)ey soil has 

 been already mentioned ; and it needs here be only re- 

 marked, that it unites more intimately the particles of the 

 clay to the prejudice of the plants, and contributes to form a 

 solid mass, into which neither the roots nor the air can pe- 

 ilctrate. 



These are the mo&t usual component parts of soil, and 

 though there are other kinds of earth, they have no influ- 

 ence on vegotation, and therefore they may be omitted. It 

 is also n-cedless to mention here that the mixture of the 

 above-mentioned component parts of black mould are not 

 general : on the contrary, that ihey are mixed according to 

 mfinite variations and gradations, and that the sum of the 

 component parts is often not the same in two fields lying 

 close to each other. For these variations and gradation» 

 are already so well known that, in the language of the agri- 

 culturists, they give occasion to difll'rent, often relative, 

 and therefore insufficient appellations. When llicy speak 

 of sandy, loamy, sharp, hot, heavy, cold, wet, and the 

 like kinds of soil, one may readily conceive from the wordsr 

 what different mixtures are to be understood under the 

 terms sandy, loamy, or wet and heavy soil ; when, at the 

 same time, the expressions sharp, hot, cold, denote the 

 same mixtures of soil in different districts. And even if 

 ve suppose that a certain fixed idea could be applied to. 

 each of these terms, it would be of little service to the 

 practical atrriculturist who looks to the improvement of hi* 

 land. Foran appellation, to be proper, ought to express the 

 sum of the component parts, that it may be seen whether 



the 



