Mosses occur in the same natural areas and historically meaningful patterns of disjunction as the vascular plants. Their ranges have resulted from slow, step-wise migration subject to topographic and climatic control in the past and to ecological conditions, past and present. The historical meaning of moss disjunctions requires explanation, however, because the fossil record is poor, spores are produced in a number and size favoring distance transport, species are somewhat more diffusely distributed than higher plants of similar range, and disjunctions are expressed mainly at the specific level rather than at a higher level obviously requiring time for evolution since primary dispersal of an ancestral form. The nature of winds, their effect on viability of diaspores, mechanisms controlling dissemination, and ecological specificity strongly argue against effective dispersal over long distances except in most unusual circumstances. The extreme antiquity of mosses and their slow rate of evolution lend significance to specific disjunctions. The moss flora of eastern North America bears the obvious mark of history, giving especially good evidence of northern, Arctotertiary origins and a later Tertiary element derived from tropical latitudes. The effects of Pleistocene glaciation are illustrated by northern and western disjuncts in the Great Lakes-St. Lawrence river area. A consideration of the Douglas Lake region of northern Michigan shows that even in a glaciated region only recently available for plant occupation the entire flora can be derived from adjacent areas, by invasion at suitable stages of succession or by survival from the flora fringing the glaciers in their last retreat. Thus, the flora offers proof that long-range dispersals have little significance in plant migrations.