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air, manifested its action in a few hours, and entirely
destroyed the plant in two days. Both these gases
acted on the leaves, affecting more or less their
colour, and withering and crisping their texture, so
that a gentle touch caused their separation from the
footstalk; and both exerted this injurious operation
when present in such minute proportions as to be
wholly inappreciable to the animal senses. After
having suffered much injury from these acid gases,
the plants, if removed in time, will recover, but with
the loss of their leaves. Hence in vegetation, carried
on in a smoky atmosphere, the plants are rarely killed
altogether, but merely blighted for the season: accordingly,
in spring vegetation recommences with its
accustomed luxuriance; and as, in many situations,
there is at that season, and through the summer,
a considerable diminution in the number of coal fires,
there will be a proportionate decrease in the production
of sulphurous acid gas, and consequently less
injury will be done to plants during that season. In
winter, too, when coal fires mostly abound, and gas
is most abundantly generated, deciduous plants are
protected from its noxious operation by suspension
of their vegetating powers; but the leaves of
evergreens, which continue to grow through that
season, are constantly exposed to its action when
present in its greatest intensity. Accordingly, in
many of the suburban districts around London, especially
in the course of the river, where new manufactories
are constantly rising up, the atmosphere is
so highly charged with noxious matters, that many
deciduous plants, and almost all evergreens, cease to
flourish, or exhibit only a sickly vegetation. In an
interesting biographical sketch of his late lamented
friend Dr. Turner, Professor Christison confirms, by
subsequent experience, the opinion formerly given
respecting the noxious operation of the sulphurous
and muriatic acid gases on plants; he describes their
action as so energetic, that, in the course of two days,
the whole vegetation of various species of plants may
be destroyed by quantities so minute as to be altogether
inappreciable by the senses. On two occasions
he was able to trace the identical effects of the
same kind of works (the black ash manufactory) on
the great scale which his friend and himself witnessed
in their researches. In one instance, the devastation
committed was enormous, vegetation being for the
most part miserably stunted, or blasted altogether,
to a distance of fully a third of a mile from the works,
in the prevailing direction of the wind.”
Mr. Lllis’s is an extremely pleasing and well-written
paper; it is full of very valuable information, collected
with industry, and arranged with care; the experiments
to which he refers are of undoubted authority,
and strictly applicable to general principles in
the way intended by their various authors. I think
they will be received as conclusive by that large class
of readers which prefers the dictum of a philosopher
to the fatigue of inquiry; but never by that limited
class—that troublesome and inquiring class—which