Archegonia and antheridia mature at different times
Sexual reproduction involves the mixing of genes from two different parents to give offspring with a genetic make-up similar to, but different from, each parent. In bryophytes the process requires the production of male gametes sperm , female gametes eggs and some means of getting the sperm to the eggs. The gametes are produced on the gametophytes. The sperm are produced within tiny, typically stalked, club-shaped structures called antheridia and you can also see bryophyte sperm referred to as antherozoids. The stalk anchors the antheridium to the gametophyte. Each antheridium produces numerous sperm.
A homosporous life history occurs in nearly all bryophytes and in most pteridophytes lower vascular plants. It is characterized by morphologically identical spores that germinate to produce bisexual both male and female gametophytes in pteridophytes but either bisexual or, more usually, unisexual either male or female gametophytes in bryophytes. Each mature gametophyte bears gametangia sex organs that produce gametes. Each antheridium male gametangium forms many motile flagellate sperm , and each archegonium female gametangium forms one nonmotile egg. Fusion of an egg and a sperm syngamy creates a zygote and restores the 2 n ploidy level. Various mechanisms prevent the fusion of eggs and sperm from a bisexual gametophyte inbreeding. For example, the sex organs may mature at different times usually antheridia mature first , or inbreeding may be chemically or genetically inhibited.
The life cycle of ferns is different from other land plants as both the gametophyte and the sporophyte phases are free living. This interactive illustrates the alternation of generations in ferns. Meiosis is a type of cell division that produces gametes — cells that contain half the number of chromosomes than the parent cell. In ferns, these cells are the spores. The typical big fern plant, what it does is, by meiosis, produces spores, and the spores have half the number of chromosomes of the big parent plant.
The sex organs of ferns are of two types. The sperm-producing organ, the antheridium , consists of a jacket of sterile cells with sperm-producing cells inside. Antheridia may be sunken as in the families Ophioglossaceae and Marattiaceae or protruding. They vary in size from those with hundreds of sperm to those with only 12 or so.