In the flora of eastern North America there are many genera that appear to be endemic there (found nowhere else), but are actually duplicated in eastern Asia, if not as to species, at any rate by plants so closely allied as to be of obviously common origin. These plants are unknown in Europe, or on our own western coast. The skunk cabbage, sassafras, twinleaf, May apple, Canada moonseed, spice-bush, ginseng, sour gum, trailing arbutus, fringe tree, lopseed and many others, all fairly common in eastern North America, are unknown between this and eastern Asia where, if not the identical species, which often happens, closely related forms are duplicated. The explanation of such discontinuous present distribution appears to be that at some time in the distant past there was a land connection between Asia and the western coast of America, the remnants of which form the Aleutian Islands, and over which there was a constant migration of plants and animals. With subsequently changing climatic conditions on our own western coast, due to warm ocean currents, most of those Asiatic migrants, or it may have been a migration in the opposite direction, were crowded out by later types which now dominate the Pacific coast. There is small chance that these plants were spread by birds, as an east-west bird migration is hardly likely. Nor is there any record that the seed of these plants, even where they might float, would survive ocean transport. Sometimes the ancestors of now widely separated species or genera once covered all or nearly all the intervening area, and again sometimes only a minute fraction of the ancient distribution is left at the present time. Our own Big Trees of California were once known to grow in England, Iceland, all through central Europe and eastern Asia, Australia, New Zealand, southern Chile, and from Texas to Alaska. In the face of such widespread occurrence in the past their present distribution over an area of a few square miles is merely a pitiful relic of ancient grandeur. Scores of cases are known where, instead of a single outpost as in the Big Trees, there are only a few widely scattered survivors from a probably much more continuous distribution in the past. In northeastern North America there grows along pond sides and fresh-water beaches the shore-weed, a relative of our common weedy plantain. The only other species, and a close relative, comes from the southern tip of South America. [Illustration: SOME OF THE COMMONER PLANTS OF THE DESERT in the Southwest. The fanlike branches at the left are the ocotillo (Fouquieria), the two short tree cacti and choya cactus (Opuntia) and the leafless tree in the central background the palo verde (Parkinsonia). (Photo by the late Edward L. Morris, released for publication here by the Brooklyn Museum.)]