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Gametophytes Pulled from Moss Cushion.When you think of moss, you normally picture the soft green "leafy" parts which are gametophytes. The gametophyte is in the haploid generation, so all its cells have only one set of chromosomes. Gametophytes use photosynthesis for energy.
Certain cells on the gametophytes develop into the sex organs. On some gametophytes, an antheridium (male) organ will develop, and other gametophytes will develop an archegonium (female). Sometimes the sex organs are located at the tips of the gametophytes. In some mosses, they are located on different parts of the plant. -
Tips Where Antheridium or Archegonium May Form.Each antheridium produces sperm cells, and each archegonium develops egg cells. A thin film of moisture is necessary for fertilization, and it can come from rain, dew or heavy humidity. The archegonium releases a chemical attractant into the thin film of water which lures the sperm. - Once the egg is fertilized, a zygote forms. The zygote is within the archegonium and contains two sets of chromosomes. It grows into a sporophyte.
- Sporophytes are the diploid generation of the moss. With chromosomes from both the egg and sperm, the sporophyte grows as a long slender stem with a capsule on top. Sporophytes grow directly from the archegonium, and they do not use photosynthesis. Instead, they draw energy from the gametophyte, which shrivels and dies as the sporophyte matures. The spores, which are haploid, develop in the capsule as the sporophyte matures.
- When the spores are ripe, the capsule breaks open and spores are released to be carried by the wind. The spores begin to form mesh-like intertwined strands of undifferentiated cells called the "protonema."
- The protonema's undifferentiated cells means that the cells are all alike and are not stem, leaf or root cells. The identical cells make up filaments from which cusps, or buds, begin to form. These cusps will grow into new moss plants as gametophytes. When growing conditions are right, the protonema can be dense, allowing many cusps to develop into a dense cushion of new gametophytes.
