The gametophyte and young sporophyte of Ampelopteris prolifera

The spores of Ampelopteris prolifera (Retz.) Copel. are bilateral and have a smooth exine and a folded perine. The gametophyte arises as a short filament which soon develops into a spatula, and ultimately becomes cordate at maturity. In overcrowded cultures the prothallus is a variously branched filament. Mature gametophytes may develop filamentous or cordate branches. Hairs with extracellular apical cap-like secretions originate both at the margin and on the surfaces of the prothallus. In old prothalli peg-like outgrowths develop on the superficial sides of the wing. The antheridia and archegonia are of the usual type found in the evolutionally advanced ferns. The development of the young sporophyte is described and illustrated. The taxonomic validity of the genus is also discussed.

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.

XXII.—The Autecology of Bracken (Pteridium aquilinum (L.) Kuhn): The Germination of the Spore, and the Development of the Prothallus and the Young Sporophyte

The rapid spread of bracken in some parts of the country has led to considerable investigation into the habits of the plant. But in almost all cases it is the spread of the adult sporophyte which has been described, and little attention has been paid to the insignificant, complementary half of the life cycle—the prothallus. Nor does any attempt appear to have been made to assess the rate of development of the prothallus and the young sporeling. A recent attempt to collect records of the occurrence of prothalli and young sporophytes in the field has shown how seldom they are found, and has emphasised the fact that little is known of the extent to which the plant spreads by the initiation of new colonies from spores (White, 1930).