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 labour is
carried out in the living economy. In the lowest organism all parts are