title: Evolutionary significance of polyploidy in the pteridophyta.
abstract: Polyploidy occurs in the heterosporous and homosporous Pteridophyta, but with a much higher frequency in the latter. Ninety-six percent of the homosporous Pteridophyta show a gametic chromosome number greater than 27, whereas 90 percent of the heterosporous ones possess a gametic chromosome number less than 28. Ultrafrequent establishment of poly- ploidy in the homosporous Pteridophy- ta appears to be necessary to create and maintain genetic variation in the face of the homozygotizing effects of habitual self-fertilization in the monoe- cious gametophytes of these plants.
authors.forename: E J
authors.initials: EJ
authors.lastname: Klekowski
authors.forename: H G
authors.initials: HG
authors.lastname: Baker