Pteridophyte geography has been examined from a number of standpoints (cf. Christ, 1910; Winkler, 1938; Tryon, 1969, 1970). A complete assessment of the significance of their geographical disjunctions would be difficult to make because of the numerous factors involved. The following discussion will concentrate upon special problems and the examples will have a strongly North American bias. Homosporous vascular plants are pteridophytes which lack micro-megaspore differentiation; all of the spores are presumably bipotential and capable of producing gametophytes with both sex organs. These pteridophytes include some of the widest ranging of all vascular plants, such as Lycopodium clavatum, Osmunda regalis, Cystopteris fragilis, and Asplenium trichomanes. The distribution patterns of pteridophytes in general are basically like those of seed plants: Narrow endemism is common, and long distance disjunctions frequently occur. One of our major concerns is whether a given disjunction may not be the result of a casual spore introduction. As Klekowski (this symposium) has pointed there are significant contrasts between ferns and seed plants, not only in means of dispersal but in their genetic apparatus as well. Some patterns of distribution, e.g. eastern AsiaNorth America and the amphitropical ones, may be related to major events in earth history. Others may be merely recent occurrences resulting from chance spores that traveled long distances. Their popularity with researchers and field botanists has caused the pteridophytes to be well collected and represented in herbaria. In the eastern United States, for example, we know the ranges of these plants so well that finding a disjunct population only 100 miles from previously known stations is considered an event. As to what we may call a disjunction, there is, of course, no set definition. As Erickson (1945) showed in a species of Clematis, the range is made up of thousands of spatially separated populations. Ehrlich and Raven (1969) assert that distances of only a few miles or less may suffice to isolate plant populations from gene flow. Here I give as examples of disjunctions separations in range of as little as 100 miles. Most of my examples (Table 1) deal with situations in which there is a large center of population and a small strongly disconnected population or group of populations. The principal seat or center will here be designated the and the small disjunct stand the outlier. Although the metropolis was not necessarily the ancestral area, in some cases it probably was. Some taxa, as we go away from their centers of abundance, simply fade out, their occurrences becoming