ompose the tissues of plants and
animals,--carbon, hydrogen, phosphorus, and the rest, which we have
already named,--are taken up by plants in mineral form alone. The food
of animals, on the other hand, consists always of organized forms. There
is no artificial process by which oxygen, carbon, and hydrogen can be
brought into a form suitable for the nourishment of animals. As oxygen,
carbon, and hydrogen, they are not food, will not sustain our life,
and human art cannot imitate their nutritious combinations. Artificial
fibrine and gluten (organic principles) transcend our power of
contrivance as far as the philosopher's stone eluded the grasp of the
alchemists. We know exactly how many equivalents of oxygen, hydrogen,
carbon, and nitrogen enter into the composition of each of the animal
elements; but we can no more imitate an organic element than we can form
a leaf. What we cannot do the vegetable world does for us. Thus we see
why it was necessary that the earth should be clothed with vegetation
before animals could be introduced. A field-mouse dies and decays, and
its elements are appropriated by the roots around its grave; and we
can easily imagine the next generations of mice, the children and
grandchildren of the deceased rodent, feasting off the tender bark which
was made out of the remains of their parent. The soil of our gardens and
the atmosphere above it are full of potential tomatoes, beans, corn,
potatoes, and cabbages,--even of peaches of the finest flavor, and
grapes whose aroma is transporting.

Plants, as well as animals, have their peculiar tastes. Cut off the
supply of phosphate of lime from a field of corn, and it will not grow.
You can easily do this by planting the same land with corn for three
or four successive years, and your crop will dwindle away to nothing,
unless you supply the ground every year with as much of the mineral as
the corn takes away from it. All plants have the power of selecting from
the soil the materials necessary to their growth; and if they do not
find them in the soil, they will not grow. It is now a familiar fact,
that, when an old forest of deciduous trees has been felled, evergreens
will spring up in their places. The old oaks, hickories, and beeches,
as any observer would discover, pass their last years in repose, simply
putting out their leaves and bearing a little fruit every year, but
making hardly any new wood. An oak may attain to nearly its full size,
in spread o