Since the discovery of apogamy in Pteris cretica by FARLOW (3) in I874, it has been observed in about I5 genera and 30 species of the Polypodiaceae. There are records of its occurrence in 3 other families of the Filicales, namely, the Osmundaceae, the Hymenophyllaceae, and the Marsiliaceae. It has been reported by SADEBECK (9) in Todea africana, by LEITGEB (7) in Osmunda regalis, by STANGE (I2) in Todea rivularis and T. pellucida, by BOWER (I) in Trichomanes alatum, by WORONIN (14) in Trichomanes Krausii, and by SHAW (ii) and STRASBURGER (13) in Marsilia. For several years I have been making a study of the prothallia of the Cyatheaceae, most of the results of which will appear in a later paper. I have had under cultivation I3 species belonging to 5 of the 7 genera. The species studied include 6 species of Alsophila, I of Hemitelia, 2 of Cyathea, 2 of Dicksonia, and 2 of Cibotium. I am indebted to Dr. J. M. GREENMAN for the determination of all the species with the exception of Alsophila Cooperi F. Muell., which was obtained from the greenhouses of Harvard University, and Cyathea muricata Wild. (Alsophila muricata Desv.), obtained from the New York Botanical Garden. In order to obtain pure cultures it was found necessary to take measures to remove foreign spores from material obtained from greenhouses where other ferns were growing. The leaves, which were collected before the sporangia had begun to open, were washed in running water and brushed rather vigorously while in the water. They were dried on sterilized glass plates and the spores which were collected were sowed on various culture media. Cultures from material handled in this way contain few if any foreign prothallia. It is not difficult to tell by the appearance of a culture whether or not there are any foreign prothallia present, owing to differences in the rate of development and in the general habit of the prothallia of different species. It is fairly easy to distinguish between the