C Fern Lab Report
July 15, 2009

The life cycle of land plants is characterized by an alteration between two phases or generation that is morphologically and functionally different. The gametophytes generation is the sexual phase of the life cycle. C-Ferns have independent haploid and diploid generations, distinct sexual types within the gametophyte generation, and they rapidly develop to full sexual maturity within two weeks. They also possess a variety of distinct visual phenotypes that can be used to perform genetic crosses (Hickok and Warne 1998). A C-Fern sporophyte is a regular diploid plant. This plant undergoes meiosis on special cells on the underside of leaves, resulting in 1N (haploid) spores. The spores undergo mitosis to produce gametophytes, of which there are two separate genders. One gender is the hermaphrodite, which is rather large and heart-shaped, and produces both eggs and a small amount of sperm. The other gametophyte gender is a very small, club-shaped male, which produces sperm only. There are no female-only gametophytes (Hickok and Warne 1998). Germination occurs three to four days and full sexual maturity is attained within six days after germination. At maturity, the gametophyte consists of a small, simple essentially flat thallus with rhizoids, vegetative cells and sexual organs (archegonia and antheridia). Archegonia are female organs that contain one egg each that lies at the base of a small neck that sticks out from the surface of the gametophyte. When mature and in the presence of water, the central canal cells burst open so that a small open canal leading to the egg is formed (Hickok and Warne 1998). The cellular contents from the central canal cells are deposited in the vicinity of the top of the open neck. In the presence of water, they too burst open and discharge swimming sperm (spermatozoids). The sperm swim rapidly in the water and are irresistibly attracted by the discharge from the archegonium. Hundreds of sperm can be seen swarming around the neck of the archegonium. One of them eventually wiggles its way down the neck and fertilizes the egg. After fertilization of the egg, the resulting diploid zygote develops rapidly by mitotic cell division and forms an embryo. Embryos are visible after a few days. In about 1-2 weeks small diploid sporophytes can be identified by the presence of roots and leaves. The gametophyte soon dies. The sporophyte grows to maturity to undergo meiosis and produce spores to begin the life cycle again (Hickok and Warne 1998). The antheridiogen is secreted by developing gametophytes controls differentiation of two distinct sexual forms of gametophytes. This is likely biosynthetically related to gibberellins and is effective at exceedingly low concentrations In the absence of antheridiogen gametophytes develop initially as heart-shaped (cordate) females with archegonia and subsequently as hermaphrodites with both archegonia and a few antheridia. In hermaphrodites, a defined meristematic region (notch meristem) is present and growth is undetermined until fertilization of an egg occurs via swimming sperm (Hickok, Warne 1998). Meristematic activity ceases soon after the fertilization event. In contrast to hermaphrodites, gametophytes that mature in the presence of antheridiogen develop into tongue-shaped males, which are small, determinate, lack a meristem and produce large numbers of antheridia. The vascular sporophyte stage consists of plants composed of a short upright stem (rhizome) with roots and leaves (fronds). Individual haploid gametophytes can be self-fertilized. Such sporophytes produce an unlimited number of genetically identical spores. If kept dry, spores remain viable for many years (Hickok and Warne 1998).

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