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74 travels throughout the archipelago. No wonder that the number of known species of trees and plants (exclusive of mosses and other low organisms) attains to the enormous figure of 2,728, distributed over 941 genera and 151 orders while it is almost certain that further investigations will raise the figure considerably, the northern portion of the country having been as yet but imperfectly explored. Of forest-trees alone, Japan—or, to be strictly accurate, the Japanese region, which includes also Korea, Manchuria, and a portion of Northern China—possesses no less than 186 species divided among 66 genera, as against the 85 species in 33 genera of Europe. The Atlantic forest region of North America is nearly as rich as Japan, having 155 species in 66 genera. The Pacific forest region of North America is poorer even than Europe, having but 78 species in 31 genera. A further very curious fact is that North-Eastern America and Japan possess 65 genera in common. Evidently there must be some powerful underlying cause connecting phenomena at first sight so capricious. Dr. Rein lays great stress on the general similarity of climatic conditions obtaining in Eastern Asia and Eastern America, on the abundant rainfall of Japan, and on the convenient stepping-stones for vegetable immigrants formed by the Kurile Islands, Saghalien, Oki, Iki, the Luchuan archipelago, and other islands both to the west and south. May we not also accept Mr. Wallace's theory, as propounded in his charming book, Island Life, to the effect that the glacial epoch had great influence in bringing about the present state of things? When the climate of the north temperate regions grew arctic, some of the trees and plants whose habitat was there must have perished, but others doubtless migrated in a southerly direction, where they could still find sufficient