CH. II.] THE ROOT. 95 



saline, and carbonaceous paiticles, of comparatively 

 little value. 



The quantity of soluble matter obtainable from a 

 soil at any one time is veiy small, seldom exceeding 

 a one-thousandth part of its weight ; and even pure 

 vegetable mould, the debris of entirely putrefied 

 plants, was found by Saussure to yield only one- 

 eleventh of soluble matter. This mould was too 

 rich for horticultural purposes, peas and beans groAvn 

 in it being too luxuriant, and they were more pro- 

 ductive in a soil containing only one-twentieth of 

 organic constituents dissolvable by water. Small in 

 amount, however, as is the soluble constituents of 

 the most fertile soils, they are necessary for the 

 \-igorous vegetation of plants, for when a soil is 

 deprived of those constituents by frequent washings 

 ^ith boiling water, it is much less fertile than before. 

 Liebig and others have most illogically concluded 

 from the smallness of the soluble extract contained 

 in a soil, that, therefore, it is of trivial impoitance ; 

 but they forget that, as fast as this extract is removed 

 from a soil by the roots of the crop, it is generated 

 again by the decomposition of the animal and vege- 

 table remains within its bosom. This is one reason 

 why fallowing is beneficial, the most easily de- 

 composing matters have been exhausted by successive 

 crops ; and by a year s rest, and exposure to the 

 putrefactive agency of the air, the more stubborn 



