of urban smoke is one of gases as well as solids, of poisonous fumes as well as inconvenient soot.
Turning now from cities, in which the growth of plants is purely for pleasure, and by no means natural or commercially profitable, we may ask what are the effects of smelting and other works from which poisonous fumes may be discharged?
Manufactories of certain chemicals, or of materials in the preparation of which poisonous substances may be volatilized, and establishments in which sulphurous ores are roasted either for the extraction of the metal or in order to obtain sulphur for the preparation of sulphuric acid, will affect surrounding vegetation more or less seriously. Even locomotive smoke injures the plants along the railroads, as anyone may observe. The herbaceous plants along the track, but quite beyond the reach of steam, often show burned spots on their leaves and stems. These are acid burns due to the fumes, of sulphur principally, discharged from the smoke-stacks of passing engines. One seldom travels over an old railway through woods or forests in which there are not many trees close to the line with branches or tops dead. Often the immediate cause of death is insects or fungi or possibly bacteria; just as tuberculosis may be the immediate cause of death in factory workers debilitated by long hours of labor under conditions unfavorable to robust health. But in many cases, locomotive smoke can be shown to be the immediate as well as the mediate cause of damage or death to trees along a railroad.
Such cases as these are, however, as unimportant, except as showing a principle, as they are at present unavoidable. On the other hand, where the prosecution of one industry results in the injury of many others, in the destruction of property, public as well as private, and in such changes in the run-off that the flow of water in streams perhaps hundreds of miles away is affected, the question becomes one of great importance. An illustration of this is found in the southeast corner of Tennessee, where, for many years, a low-grade copper ore, rich in sulphur, has been smelted. There are now two smelters in that region. The country is mountainous, the slopes naturally covered with the large-leaved mixed forest of the southern Appalachians, well watered by the frequent summer rains. The virgin forest was long ago cut for mine-timbers and for fuel in that extensive district known as Ducktown, but the second growth is also gone and, up to three years ago, nothing of any value could be cultivated within a distance of miles from these smelters. In the suit won by the state of Georgia before the Supreme Court of 'the United States, it was shown that the poisonous effects of the fumes were visible in Georgia at a distance of forty miles from these Tennessee smelters. Three and a half years ago, so hopeless was the condition of the people attempting to farm there, that they declare