Prothallia of Matteuccia nodulosa (Michx.) Fernald (Onoclea struthiopteris) and Osmunda claytoniana L. were grown from spores on soil for 4 years, under cultural conditions preventing development of sporophytes. In habit and behavior the plants strikingly resembled such liverworts as Pellia and Dendro-ceros, the prothallium attaining a size about as large as the shoots of these liverworts. Two methods of branching prevailed, true dichotomy, and formation of lateral proliferations, both large and small, from the margins and midribs on upper and lower surfaces. At the close of the 2nd year of development the prothallia began a slow death in the upper proximal parts in true liverwort fashion. In 4 years a single vigorous prothallium attained a surface growth of 120 mm. square, or a body 1600 times as large as a prothallium just large enough to bear a sporophyte. Archegonia were abundantly and continuously produced on the under side of the midrib, and frequently on the upper side. Antheridia were produced in abundance on the margins and small proliferations of the thallus and on granular appearing outgrowths on older parts of the midrib. An endophytic fungus was found in the older shoots of O. claytoniana.