The gametophyte and embryo of Polyphlebium venosum (R. Br.) Copeland (Hymenophyllaceae)

An account is given of the spore, its germination, the delicate filamentous prothallus, the reproductive organs, the embryo, and the young sporophyte of Polyphlebium verzosum. The characteristic germination, which is a modification of the four-celled or Trichomanes type, remains unchanged under various conditions. A rhizoid appears first, followed after several weeks by a filament cell. The symmetrical four-celled stage is not attained, but after 3 months another rhizoid or filament cell is often cut off from the primary cell. The monoecious gametophyte is a branching uniseriate filament and bears numerous, small, stalked antheridia, each with a simple wall, and an operculum which is raised or shed to allow the spermatozoids to escape. The archegonia, with straight necks, and tiers of four to six neck cells, are borne on special structures, the archegoniophores. The prothallus reproduces itself vegetatively by regeneration, and by gemmae which on germination produce rhizoids, filaments, and antheridia or more gemmae. The embryo is the first described for the Trichomanes group, and the investigation showed it to be unusual. There is no primary root, a single archegoniophore may bear more than one embryo, and the axis of the embryo varies in its position relative to the neck of the archegonium, possibly because the archegonia are borne in various positions on the archegoniophore. The suggestion is made that the embryo develops in a manner which gives the foot as large a contact as possible with the source of food supply. The gametophyte and embryo show some primitive characters, but the most conspicuous feature is specialization in the form of reduction as an adaptation to a moist and shady environment. A key to the Victorian Hymenophyllaceae is appended.