ion of that
which plants have assimilated into organizable matter through an energy
derived from the sun, and which is, so to say, stored up in the
assimilated products. In every internal action, as well as in every
movement and exertion, some portion of this assimilated matter is
transformed and of its stored energy expended. The steam-engine is an
organism for converting the sun's radiant energy, stored up by plants in
the fuel, into mechanical work. An animal is an engine fed by vegetable
fuel in the same or other forms, from the same source, by the
decomposition of which it also does mechanical work. The plant is the
producer of food and accumulator of solar energy or force. But the
plant, like the animal, is a consumer whenever and by so much as it does
any work except its great work of assimilation. Every internal change
and movement, every transformation, such as that of starch into sugar
and of sugar into cell-walls, as well as every movement of parts which
becomes externally visible, is done at the expense of a certain amount
of its assimilated matter and of its stored energy; that is, by the
decomposition or combustion of sugar or some such product into carbonic
acid and water, which is given back to the air, just as in the animal it
is given back to the air in respiration. So the respiration of plants is
as real and as essential as that of animals. But what plants consume or
decompose in their life and action is of insignificant amount in
comparison with what they compose.

Section XVII. CRYPTOGAMOUS OR FLOWERLESS PLANTS.

481. Even the beginner in botany should have some general idea of what
cryptogamous plants are, and what are the obvious distinctions of the
principal families. Although the lower grades are difficult, and need
special books and good microscopes for their study, the higher orders,
such as Ferns, may be determined almost as readily as phanerogamous
plants.

482. Linnaeus gave to this lower grade of plants the name of
_Cryptogamia_, thereby indicating that their organs answering to stamens
and pistils, if they had any, were recondite and unknown. There is no
valid reason why this long-familiar name should not be kept up, along
with the counterpart one of _Phanerogamia_ (6), although organs
analogous to stamens and pistil, or rather to pollen and ovule, have
been discovered in all the higher and most of the lower grades of this
series of plants. So also the English synonymous name o