308 
THE LADIES’ MAGAZINE OF GARDENING. 
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 pre¬ 
sent 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 ever¬ 
greens, 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 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 inap¬ 
preciable 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. Against the evils arising from such a vitiated atmosphere, the plan 
of Mr. Ward provides effectual protection, as the success of his own esta¬ 
blishment amply demonstrates. 
5. Condition of plants , in regard to water , in close cases , and in the free 
atmosphere. —In considering the conditions essential to vegetation, water 
may be allowed to claim the first place ; for if the vegetable exists in a 
state perfectly dry, neither the seed nor the plant can exert that action on 
the air which is essential for its development and growth. It is u owing, 
therefore, to the prevention of the escape of the moisture within the cases, 
(as Mr. Ward observes) that plants will grow in them for many months, 
or even years, without requiring fresh supplies of water: thus, the Poa 
and Nephrodium, above mentioned, grew for four years in the bottle 
without receiving one drop of fresh water, and would, (as he believes) have 
grown as many more had they not perished from an accident.” In vege¬ 
tation in the free atmosphere, the fluids, which may be absorbed either 
from the soil by the roots, or from the atmosphere by the leaves, are, in 
great part, exhaled and dissipated; but in the plant-cases they are con¬ 
densed on the inner surface of the glass roof, and fall back to the soil from 
which they were raised. In this way, both the soil and atmosphere 
possess always sufficient humidity to carry on vegetation. 
