Figure 5. The male gametophytes have structures called antheridial heads. The antheridal heads contain antheridia. Each antheridium is capable of producing numerous sperm.
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The female gametophytes contain archegonial heads. These archegonial heads contain archegonia. Each archegonium produces one egg cell. When mature, the archegonium contains a tube-like passageway that leads to the egg. When conditions are favorable and enough moisture is available, the antheridia release their sperm. The sperm uses their flagellum to swim through the moisture on the mat of moss. A sperm cell must swim to a mature archegonial head and down the tube-like passageway of the archegonium to the egg. When the haploid sperm fertilizes the haploid egg, a diploid zygote is formed. This diploid zygote grows by mitotic cell divisions directly out of the archegonium to produce the sporophyte generation.
The mature sporophyte contains a sporangium, sometimes called a capsule, on the end of a stalk called the seta. The tip of the sporangium is a pointed lid-like structure called the operculum. Within the sporangium, haploid spores are produced by the process of meiosis. When the capsule is ripe, the operculum opens and the haploid spores are released. These haploid spores then grow, by mitotic cell division, to produce a new moss gametophyte.
Figure 6. Close-up photograph of a mat of moss growing on a rock. The sporophytes are the reddish-brown stalk-like structures growing from the mat-like green gametophytes.
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