Page:Popular Science Monthly Volume 79.djvu/335

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CIVILIZATION AND VEGETATION

sheds and to conserve and control the yearly run-off, are annually placed in jeopardy by the railroads. Last year, disastrous fires in the far northwest, and the less extensive fires of Wisconsin and Minnesota in the summer preceding, only too plainly showed this. So dreadful has been the loss of human life and of property from this cause that the substitution of sparkless fuel-oil on locomotives traversing forested areas is now not only urged by the forest service, but being seriously considered by the railway companies. Until electric traction or sparkless fuel is employed, each dry season will bring its record of destruction along the tracks of civilization through forest and grazing land.

Peaching almost as far from its source as the fires accidentally set by civilization, is the destruction of vegetation by certain forms of industry. The damage is done in two ways, by drainage and by fumes. The composition of ordinary domestic drainage is disturbing enough to vegetation. I have had occasion to notice this along the shore of Monterey Bay. When I first saw these waters they were bordered on one side by the towns of Monterey and Pacific Grove, sleeping peacefully, the one after a somewhat turbulent past, the other on federal and denominational pensions. Between tide marks and further out were a fauna and flora so rich and so varied that a few years earlier, when the whole coast of California was open for such a choice, this had been selected as the best location for the Marine Biological Laboratory of Stanford University. So far as I can see, the fauna and flora are as rich to-day as then, but with the recent rapid increase in population of these two towns and the consequent increase in sewage pouring into the bay at no great distance below low-tide mark, there has been a decided increase in the quantity of diatoms living attached to the seaweeds growing between tide marks. The body of water in Monterey Bay is so very large and so thoroughly mixed by the tides, and the volume of sewage discharged into it from the towns on its shores is still so small in comparison, that the sea-water, even now, deserves to be called pure. But it is no longer perfect purity. Its increasing though still relatively slight pollution is shown by the change in the balance of the population between tide marks, by indicators exceeding in sensitiveness those of the chemical laboratory, by living things. We all know that, when pollution goes further, certain plants are no longer found in stream and bay; river and mud-flat become huge cultures in which coarse algæ and offensive bacteria flourish.

In all such changes as these, however, there is only a change, not a decrease in the value of the water as a nutrient solution. Nothing poisonous has been added to it, only substances which so abundantly nourish bacteria, blue-green algæ, diatoms and coarse green alga?, that other forms become more or less crowded out. This is so common an effect of civilization on vegetation that we think nothing of it. On the