8 THE PRACTICE OF THE 



'" -f -i 



chiefly by means of their roots, and princi- 

 pally by their fibrous or fmall roots ; for they 

 are feen, by good microfcopes, to be fpongy 

 or porous on their furface. The vegetable 

 food enters at thefe pores, and, by a wonder- 

 ful mechanifm, is thence conveyed to the fe- 

 veral parts of the plant. 



If the earth were denfe and folid, the roots 

 of plants could not penetrate into it, to col- 

 led nourimment : but all earth confids of 

 parts of various fizes, from dones and gravel, 

 to fine fand and an impalpable powder. This 

 is feen by ditto] ving earth in water, in a tall 

 glafs; wherein the earth, when broken, 

 mixed and dhTolved in water, will fettle, 

 the larged and weightied parts defcending 

 fird, and the reft in order, according to their 

 feveral refpeclive gravities; the fined and 

 lighted parts fubfiding laft of all, and fettling 

 at top. This fubdance that fettles at top is 

 very vifibie in grofs ; but the parts of it next 

 the top are fo exceedingly minute, that their 

 figure and confidence cannot be didinguifbed 

 by the naked eye, and the fined of them not 

 even by the afliftance of the greated magni- 

 fiers. It is ealy to obtain this fined part, by 

 , taking it off the top of the glafs ; or it may be 

 obtained feparate, by warning over, in the 

 manner performed by colourmen. 



All forts of land have in them fome of this 

 fine matter in different proportions. Gravelly 

 foils have but little of it; fandy foils have 



more 



