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and bears seeds in a normal way, but by the quantity of grain
and straw which the acre has actually yielded, and thus re-
duce it to a mere question of dollars and cents. This differ-
ence in object and success of two practical pursuits of similar
character, is the more necessary to be observed and fairly to
be distinguished, as their identification has principally origi-
nated the apparent but erroneous contradictions that have
been supposed to exist between the results of practical expe-
rience and the laws of scientific agriculture. A soil which
contains all the requisite nutriments for plants but am-
monia, or such matters as are capable of producing am-
monia, is, as to its productiveness, equal to a soil which con-
tains all the nutriments without exception, but its mineral
constituents in a state of combination which makes them un-
fit for ready action. Plants growing upon the one are solely
referred to the supply of ammonia from the atmosphere, and
the progress of their development must therefore be in a strict
ratio to the quantity of ammonia thus furnished to them;
'whilst the growth of the plants upon the other soil, rich in
ammoniacal compounds, must necessarily depend on the ad-
vancement of the degradation of its mineral constituents,
and is consequently in proportion to the quantity of soluble
salts, which become liberated by this process. Now, if di-
rect experiments have shown that the plants on both soils
will once reach maturity and become normally formed, it cer-
tainly proves that there is enough of ammonia in the atmos-
phere to support vegetable life, and that beyond doubt, the
ammonia of the atmosphere takes a specific part in the nu-
trition of plants generally. But there is, at the same time,
no reason to suppose that this result of observation, because
true in itself, should dictate the rules for practical operations
unless scientific agriculture be contradictory to practical farm-
ing. If this result is, in fact, of no applicability in prac-
tice, it merely proves that the development of plants should
not be made dependent on the supply of the necessary sub-
stances, but that, on the contrary, an abundance of the ne-
cessary substances should at once be offered to the plants, in
order to enable them to regulate themselves their supply, ac-
cording to their state of development; a conclusion which re-
lates most particularly to the plants we cultivate, inasmuch,
as they have to reach maturity within a certain period of
time, or will fail entirely to do so. The spirit of Liebig's
mineral theory, against which this objection has been re-
peatedly raised, makes in no wise the fertility of a soil de-
pendent on its mineral constituents exclusively, nor does
it attribute to them any preponderance over ammonia in re-