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animals alone are injured by respiring air from which
oxygen has been abstracted by previous respiration:
change of air, whether beneficial or otherwise, does
take place, for our contrivances, although they
retard, cannot preclude a change. Thus the supposed
anomalies of plants hving without air, or
without change of air, are either dissipated or softened
down: we will inquire whence arise the benefits of
this plan.
In London, the air is loaded with particles of soot,
than which there is scarcely any substance more
injurious to vegetation; a single “ smut,” as it is
usually called, causes a yellow mark wherever it has
adhered to a leaf; and the result of an atmosphere
loaded with smuts is the rapid destruction of the
leaves, so that the leaves of London trees are never
in a perfectly natural state; they differ in appearance,
colour, and health, so to speak, from the leaves of
country trees: the deleterious efiects of London
smut on the leaves influence the growth of the tree
itself, and London trees are invariably of slower
growth, and of less healthy appearance, than those in
the country. By the plan of cultivating plants in
closed vessels this injury is entirely avoided; the
smut and all solids borne by the atmosphere being
completely excluded, and forming a thick deposit on
the glass; if the vessel employed be a bell glass
inverted over the plant, then every accession of
atmospheric air must take place through the earth,
and consequently no portion of its impurities will be
m I
deposited on the plant. Mr. Ward is perfectly right,
when he attributes the sickly state of London vegetation
to “ the depressing influence of the fuliginous
matter with which the atmosphere in which he lives
is su r rou n d ed b u t it appears that other causes have
been sought in the presence of gases injurious to
vegetable life. This theory I shall now examine.
Mr. Lllis, in an excellent paper read to the Botanical
Society in June, 1839, and since pubhshed in the
Gardener’s Magazine for September,* objects to the
idea previously expressed by Mr. Ward, of the deleterious
influence of this smut or fuliginous matter;
and goes on to explain at length, that “ the real mode
in which such an atmosphere proves injurious to
vegetation was first shown by the experiments of
Drs. Turner and Christison, which were published in
the ninety-third number of the Ldinburgh Medical
and Surgical Journal. They ascertained that it is
not simply to the diffusion of fuliginous matter
through the air, but to the presence of sulphurous
acid gas, generated in the combustion of coal, that
the mischief is to be ascribed. When added to common
air, in the proportion of § ¿0 or 1^^553 part, that gas
sensibly affected the leaves of growing plants in ten
or twelve hours, and killed them in forty-eight hours
or less. The effects of hydro-chloric, or muriatic
acid gas, were still more powerful, it being found that
the tenth part of a cubic inch in 2 0 , 0 0 0 volumes of
* The Gardener’s Magazine, conducted by J. C. Loudon, vol. xv.
p . 4 8 8 .