y
flow, but contractions so minute that the best microscopes show only their
effects, and not themselves.

The spectacle afforded by the wonderful energies prisoned within the
compass of the microscopic hair of a plant, which we commonly regard as a
merely passive organism, is not easily forgotten by one who has watched
its display, continued hour after hour, without pause or sign of
weakening. The possible complexity of many other organic forms, seemingly
as simple as the protoplasm of the nettle, dawns upon one; and the
comparison of such a protoplasm to a body with an internal circulation,
which has been put forward by an eminent physiologist, loses much of its
startling character. Currents similar to those of the hairs of the nettle
have been observed in a great multitude of very different plants, and
weighty authorities have suggested that they probably occur, in more or
less perfection, in all young vegetable cells. If such be the case, the
wonderful noonday silence of a tropical forest is, after all, due only to
the dullness of our hearing; and could our ears catch the murmur of these
tiny maelstroms, as they whirl in the innumerable myriads of living cells
which constitute each tree, we should be stunned, as with the roar of a
great city.

Among the lower plants, it is the rule rather than the exception that
contractility should be still more openly manifested at some periods of
their existence. The protoplasm of Algae and Fungi becomes, under many
circumstances, partially, or completely, freed from its woody case, and
exhibits movements of its whole mass, or is propelled by the contractility
of one or more hair-like prolongations of its body, which are called
vibratile _cilia_. And, so far as the conditions of the manifestation of
the phenomena of contractility have yet been studied, they are the same
for the plant as for the animal. Heat and electric shocks influence both,
and in the same way, though it may be in different degrees. It is by no
means my intention to suggest that there is no difference in faculty
between the lowest plant and the highest, or between plants and animals.
But the difference between the powers of the lowest plant, or animal, and
those of the highest, is one of degree, not of kind, and depends, as
Milne-Edwards long ago so well pointed out, upon the extent to which the
principle of the division of labor is carried out in the living economy.
In the lowest organism all parts are compet