REMARKS ON GROWING PLANTS IN GLASS CASES. 135 



continued to grow, and turned out to be the Poa annua, and Nephro- 

 gram Fdix-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 pub- 

 lished 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 fuli- 

 ginous matter with which the atmosphere in which he lives is impreg- 

 nated." The real mode, however, 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 93rd 

 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 proportion of Tff \ r or ^J^, 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 

 hydrochloric, or muriatic acid gas, were still more powerful, it being 

 found that a 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 

 exerted this injurious operation when present in such minute propor- 

 tions 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. Ac- 

 cordingly, in spring, vegetation commences with its accustomed luxu- 

 riance; 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 ■ proportionate decrease in the production of sulphurous 

 ncid gas ; and, consequently, less injury will be done to plants during 



