Agricu Itural Chemistry. 
441 
from the soil and assimilate an increased amount of their 
necessary mineral constituents, than either the direct supply of 
the soluble minerals, or an increased amount of rain or mineral 
solvent. 
The varying produce of the unmanured plot was therefore, not 
in proportion to the amount of soluble or available soil-proper 
constituents — that is, minerals — which, even when existing in ex- 
cess, were utterly powerless, unless, either by climatic variations' 
or by direct nitrogenous manures, additional supplies of the nor- 
mally atmospheric food of plants were at the same time provided. 
True, no one Avill doubt the assertion, that " had these consti- 
tuents not been present in the soil, an increased supply of carbonic 
acid and ammonia from the air could not have had any effect on 
the crop." Such an assertion, thanks to Baron Liebig, is at the 
present day a simple truism. And, we must here again remind 
the unwary reader, that the question between Baron Liebig and 
ourselves, has never been, whether or not plants could grow 
without a due supply of mineral constituents, but, as we have 
amply shown by the copious quotations given in the earlier part 
of this paper. Baron Liebig's doctrine has been — and indeed 
many passages in his new work would indicate that it still is — 
that " if only the soil contain a sufficient supply of the mineral 
food of plants," then " the ammonia required for their develop- 
ment will be furnished by the atmosphere " ; or, as he now has it, 
when speaking of the varying produce of our unmanured plot, 
" a larger quantity of these mineral substances became active in 
the same time, and the surface of the land was thus enabled, by 
the plants groxcinr/ on it, to absorb from the air one-half more car- 
bonic acid and ammonia than in the preceding year." We, on 
the other hand, maintain, not that the mineral constituents can be 
dispensed with, but that in the ordinary course of agriculture with 
rotation, they exist relatively to other constituents in abundance, 
and that, notwithstanding this abundance, the main saleable pro- 
duce of the farm, the cereal grains, are utterly incompetent to 
yield a full agricultural crop, unless there be artificially provided, 
within the soil itself, a liberal supply of available niti'ogen, nor- 
mally the atmospheric food of plants. The question, then, is, 
not whether mineral constituents are essential to the growth of 
plants, nor whether the supply of them in manure will yield an in- 
crease of grain provided there be an excess of available nitrogen within 
the soil — for both of these postulates we need not say we fully 
assent to — but it is and has been, whether or not a liberal supply 
of the soluble mineral constituents of the cereals, to a soil suffering 
the exhaustion of an ordinary course of rotation, will enable 
the crop to assimilate in any practical and agriculturally adequate 
degree, a larger amount of nitrogen fi'om atmospheric sources ? 
