 without a microscope? Identify the two morphologically distinct kinds of gametophytes (prothallia, sing. prothallus). The larger mitten-shaped gametophytes produce both male and female sex organs. The male sex organs (antheridia, sing. antheridium) are found around the margins of the plant and near the rhizoids at the lower part of the plant. The female sex organs (archegonia, sing. archegonium) are aggregated near the growing notch, usually on the underside of the plant. Among these larger gametophytes should be numerous small, exclusively male plants. Each male gametophyte consists of numerous antheridia that give a bumpy appearance to the plant. These males develop in response to the presence of a special chemical (antheridiogen) in the medium that is secreted by older gametophytes. Can you think of any ecological or genetic advantages for such a condition in nature?
Make a wet mount that includes a few gametophytes of both types and observe your slide under the compound microscope. Draw one of each type of gametophyte, include and label the spore wall, rhizoids, photosynthetic cells, sex organs, and growing notch. What is different about these two types of gametophytes? How have the gametophytes changed from last week?
In addition, this week you should see the male gametes or spermatozoids in action. Prepare a new wet mount of several of the older male gametophytes so that you can carefully observe their antheridia, include one or two of the larger mitten-shaped gametophytes that have one to three archegonia. Over the next 5 minutes continually observe the antheridia with the compound microscope. What happens to antheridia? What does water do? Where do sperm cells come from? When you see movement, increase the magnification, and observe these small, flagellated gametes. Be very patient – give it some time. The sperm cells can move very quickly and are hard to examine unless they are caught on something or slow down. Draw and describe the shape of the sperm cells and try to locate flagella.
Once you have observed swimming sperm cells, locate the archegonia on another gametophyte. If you are patient and lucky, you will see the sperm cells swimming down the neck of the archegonium on its way to fertilize the egg inside. How can the sperm cells find their way to the egg cell? How long and how far can one sperm cell swim?
Before you put your dish back into its plastic bag, sprinkle the plants with distilled water from the squirt bottles. This water will allow the sperm cells to easily swim to the eggs in the archegonia. Next week, take a look at your cultures to see if the next generation, the diploid sporophyte, has begun to develop. The sporophyte is the product of fertilization and develops from the zygote inside of the archegonium. By next week, the sporophyte will be very small but it should be visible.
As in the beginning of the last laboratory, you should continue observing your fern gametophyte cultures. Gently remove a few of the mitten-shaped gametophytes from the dish and prepare a wet mount. Carefully observe the region close to the growing notch. If fertilization was successful last week, you may be able to see bumps at the base of older archegonia! What do you think these bumps will grow into? Where have these bumps come from?
By next week, the young sporophytes should be easily visible. Some sporophytes may be large enough to transplant from the petri dish to a terrarium containing potting soil. A 2-liter clear plastic beverage bottle can make a small, cheap mini-terrarium. When you transfer the young sporophytes, try not to take a lot of agar and separate out individual plants. If you watch your fern grow long enough (30 or more days) you may be able to find sporangia that will develop on the backside of specialized leaves. At that point, you may wish to grow spores and begin another cycle of the life history of Ceratopteris