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Although the ontogeny of fern gametophytes has a long history of morphological investigation, sex expression in ferns has only recently been studied by experimental morphologists and geneticists. Most homosporous ferns have bisexual gametophytes whose mitotically derived gametes produce a completely homozygous sporophyte after selfing (Klekowski and Baker, 1966). Wilkie's work (1956), which demonstrated self incompatibility in Pteridium aquilinum, has stimulated the use of fern gametophytes in genetic research. Klekowski and his associates (1968, 1969) used genetic and morphological criteria to characterize pteridophyte gametophytes in terms of their probability for intragametophytic (functionally bisexual) and intergametophytic (functionally unisexual) mating. This study was undertaken to determine whether the ontogeny of Dryopteris ludoviciana (Kunze) Small gametophytes differed from that reported for other dryopterid and thelypterid gametophytes (Kny, 1895; Waldemann, 1928; Nayar and Chandra, 1963), and to determine sex expression under controlled conditions. The effect of population density on sex expression was tested by culturing single isolated gametophytes and gametophytes in moderate and dense populations. The ontogeny and sex expression of Thelypteris dentata (Forsk.) E. St. John was also observed for comparison.

Gametophyte Ontogeny and Sex Expression in Dryopteris ludoviciana