ON THE CAUSES WHICH INTERFERE WITH THE 
NATURAL CONDITIONS OF PLANTS IN 
LARGE TOWNS. 
Among the causes tending to depress vegeta- 
tion in large towns, mining districts, &c., may he 
enumerated, deficiency of light , and of moisture, 
the fuliginous matter with which the atmosphere 
is always more or less loaded, and the presence of 
noxious gases . 
Enough has been said upon the all-important 
agency of light in the functions of the vegetable 
system, to convince us that we shall not err in 
