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juncus, and eriophorum. It constitutes also the principal part 
of the mould in high-lying situations, and moors where the soil 
is covered with heath (erica vulgaris). This mould is distin- 
guished from the preceding by containing a notable portion of 
phosphoric and acetic acids, which give it the property of 
reddening vegetable blues. The extractive which it contains is 
chiefly insoluble in water. This sour vegetable mould bears a 
considerable resemblance to peat, into which indeed it probably 
passes. Like it, peat contains a portion of phosphoric acid, 
and probably also of acetic acid, and an extractive readily solu- 
ble in alkalies, though but sparingly in water. Einhof has 
observed, that acid vegetable mould never occurs in those, soils 
which abound in lime, and that it is counteracted and brought 
to the state of good mould by the action of lime and marl, ft 
is clear that these manures will neutralize the acids, and thus 
enable the extractive, and other vegetable substances, to be 
acted upon by the atmosphere, to yield carbonic acid, and to 
assume those states which are proper for the nourishment of 
vegetables. It is probable that they act also directly upon the 
vegetable matter, and occasion decompositions favourable for 
vegetation. Hence the efficacy of lime when supplied to peat 
moss, and to sour lands in general. 
Upon the whole, then, it appears that plants are fed chiefly 
by that portion of vegetable matter which becomes soluble in 
water, and assumes the properties of extractive ; that the quan- 
tity of it in soil must neither be too great nor too small ; that the 
insoluble part of vegetable mould gradually assumes this state, 
either by the action of the atmosphere, or of earths or salts; 
that the presence of an acid, by countei’acting this change, 
injures the nourishing quality of vegetable mould; and that 
lime is serviceable, partly by neutr alizing the acid, and partly 
by accelerating the decomposition of vegetable mould. Animal 
manures probably supply similar materials with vegetable mould. 
They probably pr-event the formatiorr of acids, or neutralize 
them when formed : and likewise promote the decomposition 
and solubility of vegetable matter. The striking effects which 
animal manure produces on the growth of vegetables are well 
krrown; though it is not possible at present to point out the way 
in which they act. 
Such is the present state of our knowledge respecting the food 
