Ferns
Unlike mosses, ferns have a predominant sporophyte generation. The gametophyte is very small and lives for only a short time. It is photosynthetic. The plant that you would recognize as a fern is the sporophyte. By meiosis, the sporophyte produces many haploid spores. Spore cases can be seen on the underside of the fern fronds. These structures are clustered in groups called sori and contain the haploid spores.
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Each spore may develop into a tiny, heart-shaped gametophyte called the prothallium. This tiny structure is about 2 cm in diameter and contains both archegonia and antheridia. It has no vascular tissue. The archegonia produce eggs and the antheridia produce sperm. The sperm swim to the eggs in the archegonia and fertilize them. The zygote begins its development within the archegonium, but it soon grows systems of its own and separates from the gametophyte to become an independent plant, which is the sporophyte. The gametophyte then dies. The sporophyte has become independent of the gametophyte in this group of plants, and the haploid generation is reduced greatly
Because mosses and ferns require water for sexual reproduction, they are most often found in moist environments. But many live elsewhere. Some can occupy constant dry environments by reproducing as exually. Other survive temporary dry conditions. They remain dormant until water is available for sexual reproduction.
แหล่งข้อมูล : Biology living system. Page 417.
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