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Rh in the high Alleghany Mountains more than eighty years ago. No one has seen the living plant since, or knows where to find it, if haply it still flourishes in some secluded spot. At length it is found in Japan; and I had the satisfaction of making the identification. One other relative is also shown in Japan; and another has just been detected in Thibet. Whether the Japanese and the Alleghanian plants are exactly the same or not, it needs complete specimens of the two to settle. So far as we know, they are just alike. And even if some difference came to be known between them, it would not appreciably alter the question as to how such a result came to pass.

Each and every one of the analogous cases I have been detailing—and of which I could adduce very many more—raises the same question, and would be satisfied with the same answer. These singular relations attracted my curiosity early in the course of my botanical studies, when comparatively few of them were known, and my serious attention in later years, when I had numerous and new Japanese plants to study in the collections made (by Morris, Williams, and Morrow) during Commodore Perry's visit in 1853, and especially, by Mr. Charles Wright, in Commodore Rodgers's expedition in 1855. I then discussed this subject somewhat fully, and translated the facts within my reach. This was before I ever had developed the rich fossil botany of the arctic zone, before the immense antiquity of existing species of plants was recognized, and before the publication of Darwin's now famous volume on the "Origin of Species" had introduced and familiarized the scientific world with those now current ideas respecting the history of species, with which I attempted to deal in a moderate and feeble way. My speculation was based upon the former glaciation of the northern temperate zone, and the inference of a warmer period preceding (and, perhaps, following). I considered that our own vegetation, or its proximate ancestry, must have occupied the arctic and sub-arctic regions in Pliocene times, and that it had been gradually pushed southward as the temperature lowered and the glaciation advanced even beyond its present habitation; that plants of the same stock and kindred, probably ranging round the arctic zone as the present arctic species do, made their forced migration southward upon widely-different longitudes, and receded more or less as the climate grew warmer; that the general difference of climate which marks the eastern and the western sides of the continents—the one extreme, the other mean—was doubtless even then established, so that the same species and the same sort of species would be likely to secure and retain foothold in the similar climates of Japan and the Atlantic United States, but not in intermediate regions of different distribution of heat and moisture; so that different species of the same genus as in torreya, or different genera of the same group, as Redwood, taxodium and glyptostribus, or different associations of forest-trees, might establish themselves each in the region best suited to their particular