THE LADIES MAGAZINE OF GARDENING. 
307 
prior to the final change of the insect, a seedling fern and grass appeared 
on the surface of the mould. After having secured the insect, Mr. Ward 
set himself to watch the development of these plants in such a confined 
situation. He placed the bottle on the outside of the window of his 
study, where the plants continued to grow, and turned out to be the 
Poa annua , and Nephrodium Filix-mas. From this incident, so well 
improved by Mr. Ward, have arisen the results, both physiological and 
practical, which form the subject of the present communication. These 
results were published in the Companion to the Botanical Magazine, 
edited by Sir W. J. Hooker, in May 1836 ; but the incident which gave 
rise to them, and the experiments to which it led, occurred seven or eight 
years before,—that is, about eleven years from the present time (1839). 
His previous want of success in growing plants in the ordinary mode, 
Mr. Ward attributes to the “ depressing influence of the fuliginous matter 
vvdth which the atmosphere in which he lives is impregnated.” The real 
mode, however, in which such an atmosphere proves injurious to vege¬ 
tation, was first shown by the experiments of Doctors Turner and 
Christison, which were published in the ninety-third number of the 
Edinburgh 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 pro¬ 
portion of or T o~oo-o P ar t, 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 hydrochloric, or muriatic, acid gas were still more 
powerful, it being found that the tenth part of a cubic inch, in 20,000 
volumes of 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 ex¬ 
erted this injurious operation, when present in such minute proportions as 
to be wholly inappreciable by 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 con¬ 
siderable diminution in the number of coal-fires, there will be a propor¬ 
tionate decrease in the production of sulphurous acid gas; and, consequently, 
less injury will be done to plants during that season. In winter, too, 
