gametophyte of Trichomanes holopterum Kunze

The gametophyte of the filmy fern, Trichomanes holopterum Kunze, as observed in culture and in wild populations, shows two sharply defined growth forms-a filamentous, branching phase which gives rise to an upright, blade-like phase. The latter are about 1 cm tall and more or less lance-shaped in the wild, but they assume other forms under culture conditions. Usually gemmae are produced on gemmiphores at the apices of the upright blades. Antheridia are formed on both filaments and blades. Archegonia occur only on cushions formed by the filaments. After these cushions are formed, upright blades identical with those produced from the filaments arise from them. The rhizoids are darkly pigmented and very short. Described are unusual secretory "glands" borne upon the filaments and blade bases. These structures are without doubt homologous to and modified from rhizoids with which they intergrade. They are thus not readily comparable with other types of glands known among fern gametophytes. The gametangia and embryos appear to conform to previous descriptions for the family, Hymenophyllaceae. Spore germination is of the four-celled type, three cells cutting off, one at each of the corners of the triradiate spore. Aposporous gametophytic outgrowths were observed in culture on both old and young sporophyte fronds. The specializations of this gametophyte are discussed in terms of possible adaptive value and systematic implications. The species is "bryophytic" in the sense that its gametophyte is the "dominant" generation, more abundant than the sporophyte and self-reproducing in its habitat.