Dr. J.G. Cooper, in an interesting article prepared by him at the expense of the Smithsonian Institute, on the distribution of the forests and trees of North America, with notes and observations on the physical geography, climate, etc., of the country, after classifying, arranging, and tabulating the results of the various observations forwarded to that institution, indulges in the following general observations: "We have with a tropical summer a tropical variety of trees, but chiefly of northern forms. Again, with our arctic winters, we have a group of trees, which, though of tropical forms, are so adapted to the climate as to lose their leaves, like the northern forms, in winter. But, here, it must be distinctly understood, is no alteration _produced_ by climate. Trees are made for and not _by_ climate, and they keep their characteristics throughout their whole range, which with some extends through a great variety of climate." The italics are the authors, and we suppose he means by "tropical" and "arctic," the sub-tropical and sub-arctic. In making his general observations, he had before him large collections of the leaves, fruits, bark, and wood of trees from all parts of the United States, including portions of Mexico, the Canadas and Alaska, and extending from the Atlantic to the Pacific. But one of the most important elements--in fact, the _most_ important--is wanting in the tables before us, and that is, the elevation at which these thousands of specimens were obtained. So great an oversight as this should not have occurred, although it may not have been entirely Dr. Cooper's fault. He had his materials to work upon, and may have done the best that any one could with them. And yet it is just as important to know at what _elevation_ a particular tree grows in its own plant zone, as to know whether it comes from a sub-arctic or sub-tropical region.