a crystal of salt in brine: but, on closer examination, it turns out
to be something very different. For the crystal of salt grows by
taking to itself the salt contained in the brine, which is added to
its exterior; whereas the plant grows by addition to its interior: and
there is not a trace of the characteristic compounds of the plant's
body, albumin, gluten, starch, or cellulose, or fat, in the soil, or
in the water, or in the air.

Yet the plant creates nothing; and, therefore, the matter of the
proteins and amyloids and fats which it contains must be supplied to
it, and simply manufactured, or combined in new fashions, in the body
of the plant.

It is easy to see, in a general way, what the raw materials are which
the plant works up, for the plant get nothing but the materials
supplied to it by the atmosphere and by the soil. The atmosphere
contains oxygen and nitrogen, a little carbonic acid gas, a minute
quantity of ammoniacal salts, and a variable proportion of water. The
soil contains clay and sand (silica), lime, iron, potash, phosphorus,
sulphur, ammoniacal salts, and other matters which are of no
importance. Thus, between them, the soil and the atmosphere contain
all the elementary bodies which we find in the plant; but the plant
has to separate them and join them together afresh.

Moreover, the new matter, by the addition of which the plant grows, is
not applied to its outer surface, but is manufactured in its interior;
and the new molecules are diffused among the old ones.

The grain of wheat is a part of the flower of the wheat plant, which,
when it becomes ripe, is easily separated. It contains a minute and