1. Under favorable conditions the plate stage follows very quickly after germination; there is ordinarily no filament left at the base of the prothallium. The mature prothallium usually is longer and the cushion heavier than in the Polypodiaceae. Forking of the cushion of the prothallium occurs frequently in old cultures, and in certain species may occur in relatively young prothallia. 2. Multicellular hairs were found to develop more or less abundantly on mature prothallia of all species of Alsophila, Hemitelia, and Cyathea, and to occur rarely on Lophosoria. None were found on Thyrsopteris, Culcita, Cibotium, or Dicksonia. The multicellular hair arises from a special initial, a wedge-shaped cell cut from the anterior face of a superficial cell near the apical meristem. The hairs are found on both dorsal and ventral surfaces, on or near the cushion, but not on the margin. The hairs may reach a length of 2 mm. 3. The wall of the antheridium typically consists of five cells: an oblique basal cell, a lower ...