216 ON CLOSELY GLAZED CASES. 



require rest, and obtain it in some countries by the rigour of winter, 

 and in others by the scorching and arid heat of summer. 



Plants in large Towns suffer from deficiency of light, dryness of 

 the atmosphere, fuliginous matter with which the air of large towns 

 is always more or less loaded, and the evolution of noxious gases from 

 manufactories. 



Of all these atmospheric causes tending to depress vegetation in 

 large towns, Mr. Ward is of opinion that the fuliginous matter is the 

 most influential. Sulphurous acid gas generated in the combustion of 

 coal, when added to common air in the proportion of toVo- or to-Wo- 

 part, has sensibly affected the leaves of growing plants in 10 or 12 

 hours, and killed them in 48 hours or less ; and hydrochloric or mu- 

 riatic acid gas, in the proportion of T V of a cubic inch to 20,000 

 volumes of air, produced an injurious effect in a few hours, and entirely 

 destroyed the plant in two days. Such were the results of experi- 

 ments made by Drs. Turner and Christison, and quoted in an article 

 on Mr. Ward's plant-cases, by the late Daniel Ellis, Esq. Mr. Ward 

 has no doubt of the correctness of the experiments quoted ; but he 

 contends " that it yet remains to be proved that there exists generally, 

 in the atmosphere of London or other large cities, such a proportion 

 of these noxious gases as sensibly to affect vegetation." In proof of 

 this, Mr. Ward refers to the hundreds of geraniums and other plants, 

 seen in the windows of shops and small houses in numerous parts of 

 London, " growing very well, and without any crisping or curling of 

 their leaves, care being taken in these instances to keep the plants per- 

 fectly clean, and free from soot." Now, Mr. Ward's cases " can, and 

 do, exclude the fuliginous portion of the atmosphere," and hence the 

 thriving of the plants grown in them. These cases, however, cannot 

 exclude gases mixed with the atmosphere ; from which it may be 

 concluded that the proportion in which deleterious gases exist in it is 

 not such as to be injurious to vegetation, nothing like so much so as 

 the " acidulous emanations" which issue from the numerous chimneys 

 of the chemical factories in a certain part of Glasgow, and which our 

 correspondent in that city informs us " wither up the leaves in the 

 course of a few hours," while the fuliginous particles, according to the 

 same correspondent, are not concerned in injuring vegetation. 



Mr. Ward next shows, by quotations from Turner's Elements of 

 Chemistry, and from other works, that the constant tendency of the 



