hen,
the primary and a mental form of life is merely an individual mass of
protoplasm in which no further structure is discernible. Well, then, has
protoplasm been called the "universal concomitant of every phenomena of
life." Life is inseparable from this substance, but is dormant unless
excited by some external stimulant, such as heat, light, electricity,
food, water, and oxygen.

Although we have seen that the life of the plant as well as of the
animal is protoplasm, and that the protoplasm of the plant and that of
the animal bear the closest resemblance, yet plants can manufacture
protoplasm out of mineral compounds, whereas animals are obliged to
procure it ready made, and hence in the end depend on plants. "Without
plants," says Professor Orton, "animals would perish; without animals,
plants had no need to be." The food of a plant is a matter whose energy
is all expended--is a fallen weight. But the plant organism receives it,
exposes it to the sun's rays, and in a way mysterious to us converts the
actual energy of the sunlight into potential energy within it. It is for
this reason that life has been termed "bottled-sunshine."

The principal food of the plant consists of carbon united with oxygen to
form carbonic acid, hydrogen united with oxygen to form water, and
nitrogen united with hydrogen to form ammonia. These elements thus
united, which in themselves are perfectly lifeless, the plant is able to
convert into living protoplasm. "Plants are," says Huxley, "the
accumulators of the power which animals distribute and disperse."
Boussengault found long since that peas sown in pure sand, moistened
with distilled water and fed by the air, obtained all the carbon
necessary for their development, flowering, and fructification. Here we
see a plant which not only maintains its vigor on these few substances,
but grows until it has increased a millionfold or a million-millionfold
the quantity of protoplasm it originally possessed, and this protoplasm
exhibits the phenomena of life. This and other proof led M. Dumas to
say: "From the loftiest point of view, and in connection with the
physics of the globe, it would be imperative on us to say that in so far
as their truly organic elements are concerned, plants and animals are
the offspring of the air."

Schleiden,[8] speaking of the haymakers of Switzerland and the Tyrol,
says: "He mows his definite amount of grass every year on the Alps,
inaccessible to cattle, and give