which scarcely suffices to deprive the polished granite of
Heidelberg of its lustre.

Some soils abound in silicates so readily decomposable, that in
every one or two years, as much silicate of potash becomes soluble
and fitted for assimilation as is required by the leaves and straw
of a crop of wheat. In Hungary, extensive districts are not uncommon
where wheat and tobacco have been grown alternately upon the same
soil for centuries, the land never receiving back any of those
mineral elements which were withdrawn in the grain and straw. On the
other hand, there are fields in which the necessary amount of
soluble silicate of potash for a single crop of wheat is not
separated from the insoluble masses in the soil in less than two,
three, or even more years.

The term fallow, in Agriculture, designates that period in which the
soil, left to the influence of the atmosphere, becomes enriched with
those soluble mineral constituents. Fallow, however, does not
generally imply an entire cessation of cultivation, but only an
interval in the growth of the cerealia. That store of silicates and
alkalies which is the principal condition of their success is
obtained, if potatoes or turnips are grown upon the same fields in
the intermediate periods, since these crops do not abstract a
particle of silica, and therefore leave the field equally fertile
for the following crop of wheat.

The preceding remarks will render it obvious to you, that the
mechanical working of the soil is the simplest and cheapest method
of rendering the elements of nutrition contained in it accessible to
plants.

But it may be asked, Are there not other means of decomposing the
soil besides its mechanical subdivision?--are there not substances,
which by their chemical operation will equally well or better render
its constituents suitable for entering into vegetable organisms?
Yes: we certainly possess such substances, and one of them, namely,
quick-lime, has been employed for the last century past in England
for this purpose; and it would be difficult to find a substance
better adapted to this service, as it is simple, and in almost all
localities cheap and easily accessible.

In order to obtain correct views respecting the effect of quick-lime
upon the soil, let me remind you of the first process employed by
the chemist when he is desirous of analysing a mineral, and for this
purpose wishes to bring its elements into a soluble state. Let the
mineral to