Up until I933 published accounts of Michigan bryophytes have dealt chiefly with three sections of the State, namely (I) the southern end of the lower Michigan peninsula-the region centering about the University of Michigan at Ann Arbor, Michigan State College at East Lansing, and Climax (in Kalamazoo County, home of Mr. H. R. Becker); (2) the northern end of the lower peninsula together with Mackinac Island and adjoining parts of the northern peninsulathe region centering about the University of Michigan Biological Station, at Douglas Lake; and (3) Isle Royale-situated along the northern shore and toward the western end of Lake Superior, about 50 miles north of the Keweenaw Peninsula, nearest point on the Michigan mainland. It is only within the past twr years that much has come to be written regarding the bryophyte flora of the uppeo Michigan peninsula. In a state the size of Michigan, which extends from north to south a distance of more than 400 miles and a nearly equal distance from east to west, it is inevitable that climatic conditions should vary considerably between the more remote sections. The effect upon vegetation of such climatic dissimilarities is very strikingly exemplified by the contrast between the climax forests of broadleaf deciduous trees which characterize the more southerly portions of the State and the forests of mixed evergreen and deciduous trees which represent the climax northward. It is seen in the occurrence of certain plants along the shores of Lake Superior which occur nowhere else in Michigan. But fully as important as climate, if not more so, in its effect upon the distribution within this region of many bryophytes, more especially of those species which grow on mineral soils, is the great diversity of topographic and geological conditions which is found within the State. During the fifteen summers that the writer has been connected with the Biological Station, the bryophyte flora of the surrounding country has come to be pretty well known, approximately 300 species of liverworts and mosses having been recorded from the region within 25 miles of the Station. A brief resume of the kinds of habitat available in this area was given in an earlier paper (2). Suffice it to say that here, as elsewhere throughout the greater part of the lower Michigan peninsula, the prevailing mineral substrata are gravel and sand. Almost the only rock habitats to be found within convenient collecting distance of the Station are the dolomite cliffs and ledges on Mackinac Island. There, as would be expected, occur certain rock-inhabiting, or saxicolous, species which have been found nowhere else in the Douglas Lake region; but the number of these, scarcely more than a dozen, at first thought seems surprisingly small. This is doubtless to be accounted for partly by the prevailingly alkaline reaction