o a new generation of plants.

The oxygen which marine animals withdraw in their respiration from
the air, dissolved in sea water, is returned to the water by the
vital processes of sea plants; that air is richer in oxygen than
atmospheric air, containing 32 to 33 per cent. Oxygen, also,
combines with the products of the putrefaction of dead animal
bodies, changes their carbon into carbonic acid, their hydrogen into
water, and their nitrogen assumes again the form of ammonia.

Thus we observe in the ocean a circulation takes place without the
addition or subtraction of any element, unlimited in duration,
although limited in extent, inasmuch as in a confined space the
nourishment of plants exists in a limited quantity.

We well know that marine plants cannot derive a supply of humus for
their nourishment through their roots. Look at the great sea-tang,
the Fucus giganteus: this plant, according to Cook, reaches a height
of 360 feet, and a single specimen, with its immense ramifications,
nourishes thousands of marine animals, yet its root is a small body,
no larger than the fist. What nourishment can this draw from a naked
rock, upon the surface of which there is no perceptible change? It
is quite obvious that these plants require only a hold,--a fastening
to prevent a change of place,--as a counterpoise to their specific
gravity, which is less than that of the medium in which they float.
That medium provides the necessary nourishment, and presents it to
the surface of every part of the plant. Sea-water contains not only
carbonic acid and ammonia, but the alkaline and earthy phosphates
and carbonates required by these plants for their growth, and which
we always find as constant constituents of their ashes.

All experience demonstrates that the conditions of the existence of
marine plants are the same which are essential to terrestrial
plants. But the latter do not live like sea-plants, in a medium
which contains all their elements and surrounds with appropriate
nourishment every part of their organs; on the contrary, they
require two media, of which one, namely the soil, contains those
essential elements which are absent from the medium surrounding
them, i.e. the atmosphere.

Is it possible that we could ever be in doubt respecting the office
which the soil and its component parts subserve in the existence and
growth of vegetables?--that there should have been a time when the
mineral elements of plants were not reg