more than probable
that, when the vegetable world is thoroughly explored, we shall find all
plants in possession of the same powers, at one time or other of their
existence.

I am not now alluding to such phenomena, at once rare and conspicuous, as
those exhibited by the leaflets of the sensitive plant, or the stamens of
the barberry, but to such more widely spread, and, at the same time, more
subtle and hidden, manifestations of vegetable contractility. You are
doubtless aware that the common nettle owes its stinging property to the
innumerable stiff and needle-like, though exquisitely delicate, hairs that
cover its surface. Each stinging needle tapers from a broad base to a
slender summit, which, though rounded at the end, is of such microscopic
fineness that it readily penetrates, and breaks off in, the skin. The
whole hair consists of a very delicate outer case of wood, closely applied
to the inner surface of which is a layer of semifluid matter, full of
innumerable granules of extreme minuteness. This semifluid lining is
protoplasm, which thus constitutes a kind of bag, full of a limpid liquid,
and roughly corresponding in form with the interior of the hair which it
fills. When viewed with a sufficiently high magnifying power, the
protoplasmic layer of the nettle hair is seen to be in a condition of
unceasing activity. Local contractions of the whole thickness of its
substance pass slowly and gradually 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 cornfield.

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 the