A review of the hypotheses of various writers as to the origin and spread of the floras of the tropical Pacific Islands, with emphasis on ecesis rather than on migration possibilities, and an application of this idea to Pacific paleogeography, with the author''s opinions that the older idea of the relative permanence of the Pacific Ocean basin remains possible of assumption; that the various islands and island groups within it are probably volcanic extrusions very little, if at all, more considerably connected with one another than they are at present; that they appeared in late Mesozoic or in early to mid-Tertiary times; that the emergent islands received streams of overseas immigrant germules from all sides of the continental border of the Pacific, and that certain of these germules became established to form the ancestors of the present insular floras.