INTRODUCTION. 
XXI 
atmosphere in which he lives is surrounded : ” but it ap- 
pears that other causes have been sought in the presence 
of gases injurious to vegetable life. This theory I shall 
now examine. 
Mr. Ellis, ^ in an excellent paper read to the Botanical 
Society, in June, 1839 , and published in the fifteenth vo- 
lume of the ^ Gardener’s Magazine,’ objects to the idea 
previously expressed by Mr. Ward, of the deleterious in- 
fluence 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 ‘ Edin- 
burgh Medical and Surgical Journal.’ They ascertained 
that it is not simply to the diflusion 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 he ascribed. When added to common air, in the 
proportion of -9 oW or to^-^ 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 power- 
ful, it being found that the tenth part of a cubic inch in 
20,000 volumes of ah’, 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 co- 
lour, and withering and crisping their texture, so that a 
* This estimable and highly intelligent gentleman has since died, lamented 
by all who knew him. 
