172 AMERICAN POMOLOGY. 



among one another in the open air, prevents the danger 

 that would ensue in a confined situation. The accidental 

 production of sulphurous and other poisonous gas, or the 

 escape of smoke from the flues^ or from the tobacco-pan 

 in the green-house, sometimes produces the most disas- 

 trous effects upon the plants subjected to their action. 

 So, in crowded cities, it often happens that the effects of 

 coal smoke and other gases, generated in the furnaces and 

 manufactories, are very injurious to vegetation. The coal 

 soot falls in flakes like lamp-black, which covers the sur- 

 face and obstructs the transpiration of the stomata, and 

 thus seriously affects the health of plants in such situations. 



The action of miasmata, suggested by Lankester, is as 

 obscure in the effects produced upon plants as in those up- 

 on animals. The presence of these atmospheric conditions 

 cannot be detected by any of our tests, nor can their ef- 

 fects be prevented by any means in our power ; we know 

 little or nothing about their characters, yet we cannot de- 

 ny their existence : finally, they serve as a very convenient 

 explanation, though a very unsatisfactory one, for the in- 

 cursions of maladies that are of an obscure or unknown 

 character. Whether of a miasmatic nature or not, no one 

 can deny the existence of certain atmospheric conditions, 

 wnich appear to produce disastrous effects upon some of 

 our vegetable productions whether these be inherent to 

 the air itself, or are only conveyed by it from one place to 

 another. The inexplicable potato disease may owe its 

 origin and diffusion to such a cause, and the grape malady, 

 which appears to be dependent upon atmospheric causes, 

 may at least be carried from one vine to another upon 

 this medium, in the form of the minute spores or seeds 



