ly from point to point, and give rise
to the appearance of progressive waves, just as the bending of
successive stalks of corn by a breeze produces the apparent billows of a
corn-field.

But, in addition to these movements, and independently of them, the
granules are driven, in relatively rapid streams, through channels in
the protoplasm which seem to have a considerable amount of persistence.
Most commonly, the currents in adjacent parts of the protoplasm take
similar directions; and, thus, there is a general stream up one side of
the hair and down the other. But this does not prevent the existence of
partial currents which take different routes; and, sometimes, trains of
granules may be seen coursing swiftly in opposite directions, within a
twenty-thousandth of an inch of one another; while, occasionally,
opposite streams come into direct collision, and, after a longer or
shorter struggle, one predominates. The cause of these currents seems
to lie in contractions of the protoplasm which bounds the channels in
which they flow, but which are 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 dulness 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.