rtion of small potatoes is sure to be the consequence. After a
certain stage of growth, new tubers are formed each time the soil is
disturbed; these never fully develop, they rob those first formed, and
make the crop much inferior to what it should be. By the mode of culture
described, the ground is made warm and mellow close up to the
seed-potatoes, the roots soon fill the whole hill, and tubers are formed
that have nothing to do but to grow. The writer is aware flat culture
has strong advocates; but, after many experiments, he is convinced that
hills are much the best.

PLASTER.

However much lime or other fertilizers may be applied to the soil, still
great benefit is derived from the use of plaster, (sulphate of lime.)

After all, plaster is the main dependence of the potato-grower, a help
on which he may rely with the utmost confidence. Astonishing results are
obtained from its use, when applied in a proper manner. The writer has
seen a field, all of the same soil, all prepared alike, and all planted
with the same variety at the same time, on one half of which, that had
no plaster, the yield was but sixty bushels per acre, and many rotten;
the other part, to which plaster was applied in the manner hereafter
explained, yielded three hundred and sixty bushels per acre, and not an
unsound one among them.

The action of plaster is often puzzling. From the fact that where land
has been strongly limed, a small quantity of plaster applied shows such
decided benefit, there would seem plausibility in Liebig's theory that
its effects must be traceable not to the lime, but to the sulphuric
acid. The ammonia in rain-water in the form of carbonate (a volatile
salt) is decomposed by plaster, the sulphuric acid having greater
affinity for it, thus forming two new compounds, sulphate of ammonia and
carbonate of lime. But as arable soil has the same property of absorbing
ammonia from the air and rain-water, and fixing it in the same or even a
higher degree than lime, there is only the sulphuric acid left to look
to for an explanation of the favorable action of plaster on the growth
of plants.

It is found that plaster in contact with soil undergoes decomposition,
part of the lime separating from the sulphuric acid, and magnesia and
potash taking its place, quite contrary to the ordinary affinities.

These facts show that the action of plaster is very complex, and that it
promotes the distribution of both magnesia and potash