row Peas on a hot shallow sand; and Potatoes
and Carrots on a cold clay; and Asparagus on a shallow bed of pebbles
and potsherds. To the gardener the chemistry of crops is a matter of
great importance, because he cannot restrict his operations to such
crops as the land is particularly adapted for, but must endeavour to
make the land capable of carrying more or less of all the vegetables
and fruits that find a place in the catalogue of domestic wants. That he
must fail at certain points is inevitable; nevertheless his aim will be,
and must be, of a somewhat universal kind, and a clear idea of the
relations of plants to the soil in which they grow will be of constant
and incalculable value to him.

We are bound to say at the outset that a complete essay on the chemistry
of vegetation is not our purpose. We are anxious to convey some useful
information, and to kindle sufficient interest to induce those who have
hitherto given but slight attention to this question to inquire further,
with a view to get far beyond the point at which we shall have to quit
the subject.

Plants consist of two classes of constituents--the Inorganic, which may
be called the foundation; and the Organic, which may be considered the
superstructure. With the former of these we are principally concerned
here. A plant must derive from the soil certain proportions of silica,
lime, sulphur, phosphates, alkalies, and other mineral constituents, or
it cannot exist at all; but, given these, the manufacture of fibre,
starch, gum, sugar, and other organic products depends on the action of
light, heat, atmospheric air, and moisture, for the organic products
have to be created by chemical (or vital) action within the structure,
or, as we sometimes say, the tissues of the plant itself. To a very
great extent the agencies that conduce to the elaboration of organic
products are beyond our control (though not entirely so), whereas we can
directly, and to a considerable degree, provide the plant with the
minerals it more particularly requires; first, by choosing the ground
for it, and next by tilling and manuring in a suitable manner. A clay
soil, in which, in addition to the predominating alumina, there is a
fair proportion of lime, may be regarded as the most fertile for all
purposes; but we have few such in Britain, our clays being mostly of an
obdurate texture, retentive of moisture, and requiring much cultivation,
and containing, moreover, salts of iron in pro