The gametophyte is the dominant stage in bryophytes. The reproductive structures develop in the apical region of most mosses. In some species, both the sperm- producing structure (antheridium) and the egg-producing structure (archegonium) are produced on the same plant while in others only one or the other occur on a single plant.

Examine the tip of a leafy moss. If the tip has a flat cluster of leaves, the plant is a male gametophyte, and the antheridia are located in this flat circlet of leaves. If the leaf arrangement at the tip is no different than the rest of the stem, the plant is probably a female gametophyte, and the archegonia occur hidden among the leaves at the tip. Moisture drops splattering over the plants carry sperm from male plants to the female. As a droplet of rain sits in the cup-like circlet of leaves on the male, sperm are released into it. Subsequent ricocheting or splattering of these droplets results in some of them landing on female plants. The motile sperm then swim through the water to the archegonia.

Compare your fresh wet-mount with the prepared slides of plants with antheridia and those with archegonia. Examine a slide showing antheridia. An antheridium is broadly or narrowly oval with a one cell layered outer coat, the jacket layer. Within this layer are a tightly packed group of cells that produce sperm. How does this structure compare with gametangia found in algae? Among the antheridia are leaf-like structures or slender filaments known as paraphyses. These are erect and hair-like with expanded, club-like tips.
What function do you suppose these structure serve among the gametangia? What is the function of the jacket layer?

If your wet-mount slide contains a plant with antheridia, use a needle to tease out a few by pressing at the base of the head. After a while, mature antheridia should probably rupture and discharge sperm. Observe periodically to see if sperm are released.

Examine a prepared slide of a gametophyte with archegonia. This is shaped somewhat like a hollow bowling pin. An archegonium consists of a swollen base called the venter, which contains a single egg cell. Above the venter is a slender tube of cells called the neck. The archegonium exudes a chemical that attracts sperms cells that swim down the neck to the egg. Syngamy occurs and the zygote forms within the venter. How many cells thick does the archegonium appear to be?

The zygote develops into the embryo by numerous cell divisions within the archegonium. As the embryo continues to grow, the young sporophyte develops a foot that anchors the sporophyte into the archegonium and provides a nutritional link to the gametophyte. At this time the archegonium will also expand in size and become large enough to hold the young sporophyte for a time. Finally, the growth of the sporophyte outpaces that of the expanding archegonium and the archegonium splits into a top and bottom piece. The sporophyte continues growth producing a tall stalk with a single sporangium on top. The top part of the old archegonium covers the sporangium until close to maturity and is called the calyptra.

Examine moss gametophytes for sporophytes. Look for calyptras. Examine the sporangia. Prepared slides are available to examine the internal structure of the sporangium. Within this structure are cells that undergo meiosis and produce haploid spores. These spores have a hard protective wall and may withstand drought for long periods. The spores will germinate and produce a filamentous structure called the protonema. Note the similarity of this structure to a filamentous green alga. As a protonema matures it produces buds that develop into leafy gametophytes.

• What is the advantage of height for a sporophyte?
• What limits height among gametophytes?
• How difficult would it be for the exchange of gametes between individuals if gametophytes were considerably taller? 
• Is there a disadvantage for plants with moss-like reproduction to have the gamete-producing plant also be the principal photosynthetic generation?