" P. H. F.," Babylon, N. Y., says : "On the subject of the sanitary effect of our best native hardy forest trees, as to planting in cities, etc., I have made inquiries from different sources and can find nothing on the subject except the observations on Eucalyptus globulus. Should the subject be agitated no doubt good would result. Any information you may be able to give me will be thankfully received".

[Trees, in common with vegetation generally, have a sanitary influence by absorbing the carbonic acid from the atmosphere, which, in excess, would be fatal to animal life. It is believed that the atmosphere of the earth was at one time much more highly charged with carbonic acid than now, that much of it was taken up by metals which thus became carbonates, and that the chief mission of the luxurious vegetation which clothed the earth's surface in the carboniferous era was to clear from the atmosphere the large amount of carbon the atmosphere contained, and which we now have in the form of coal. If the carbon now confined in coal, and which was once in the atmosphere, were to be let loose into the atmosphere, and with oxygen become carbonic acid, no creature could live. One great mission of vegetation is to correct this.

But our correspondent evidently has in his mind the influence of trees in removing disease germs and making places healthy in our time that are notoriously unhealthy. It has been thought that the resinous odors given off by pine trees have an influence on reducing epidemics, and that Eucalyptus, or Blue gum, has a similar influence. But our experience with yellow fever showed it worse in some pine districts in the South than anywhere, and the miners in the Blue gum districts of Australia suffer from fevers as bad if not worse than where the Blue gum does not grow.

The only point left is the statement that fever prevailed in the Pontine marshes near Rome, and that there has been none since the large plantations were made there. Whether the fever has so utterly left as represented we do not know, because it is every day experience that newspaper statements are not usually given with that exactness which science demands. Rapid growing trees, however, absorb immense amounts of moisture. They would make a marsh dry. If any diseases prevailed from excess of moisture, any rapid growing tree would have the same effect. - Ed. G. M].