The great bulk of all vegetation is derived from the atmosphere. The air
is always loaded with watery vapor, and it contains a vast quantity of
carbonic acid gas, which furnishes the chief material for the woody
fibre of all plants, for the starch, sugar, gums, oils, and other
valuable compounds produced by them. Nitrogen, also, is one of the large
constituents of the air, and is found in it likewise in the form of
ammonia. It is wonderful to reflect that of all the vegetable
productions of the earth--its vast forests, the flowery clothing of its
boundless prairies, the immeasurable productions raised by the industry
of the whole human race in its countless fields of labor--that of all
this mighty growth which covers and adorns the face of the whole solid
globe, more than ninety-five hundredths are derived exclusively from the
atmosphere. This vast ocean which surrounds the earth, in which we are
immersed, and which is actually the breath of life to us, indispensable
to our existence during every moment of our lives, is also the great
reservoir from which the mighty vegetable world draws almost the whole
of its substance. While we are inspiring the invisible fluid, and with
every breath renewing the ruddy currents of the heart and sending them
glowing with warmth and vitality to all the extremities of the frame,
every leaf in the mighty forest, and every herb, and flower, and blade
of grass on the surface of the whole earth, is maintaining a similar
commerce with the air, drawing from its boundless stores of carbon,
piling up cell upon cell and adding fibre to fibre, until trunk, and
branch, and stem, and leaf, with all the gorgeous productions of
vegetable life, stand forth in their maturity, filling the bosom of the
conscious atmosphere with wonderful creations of beauty and fruits of
joy.
But in fact the atmosphere is only an appendage to the solid earth,
existing in that plastic form which is necessary to the creation both of
animal and vegetable life. It is her breath, by which, as the minister
of God, she breathes life into the nostrils of men and animals, and
imparts vitality and growth to all plants. But in this life-giving
process, she furnishes also a part, minute though it be, of her own
proper substance. Consume with fire the trees of the forest, or the
grass of the prairie, and though the greater part of the burning mass
will disappear and mingle with the air from which it came, there will
yet remain the ashes, which cannot be dissipated, but must return again
to the earth which gave them. These solid constituents of plants are the
contributions of the soil; and though they seem to be comparatively
inconsiderable, yet when taken in connection with the large operations
of agriculture continued through a series of years, they become so great
as to be of the utmost importance. They perform an interesting part in
the economy of vegetable life, for they are to the plant what the bones
are to the animal. In the stalks of wheat and Indian corn, as indeed of
all the grasses, the flinty surface is constituted largely of silex; as
the shells of crustacea and the bones of animals are composed mostly of
lime. Without these earthy substances, nothing that grows from the soil
can come to perfection. They are equally important to animals and to man
himself, who receives them from the vegetable world and assimilates them
in his own marvellous organization--building up his bony frame with the
lime of the earth; filling his veins with its iron; constructing the
very seat and citadel of the soul, and flashing its spiritual mandates
through the nerves, by the help of the phosphorus which he derives from
the soil through the elaboration of plants and inferior animals.