How-To-Do-It
Growing Fern Gametophy in the Classroom Christopher R. Matlack
Until recently, I had found it very 2. Back in the lab, put the soil in a able to grow and see the fem gameto- difficultto teach the conceptof alterna- clear plastic sandwich container phyte growth form (Figure2) has been tion of generations in the primitive (23 cm x 23 cm x 8 cm) that a big help to my students in facilitating Downloaded from http://online.ucpress.edu/abt/article-pdf/60/8/594/48698/4450556.pdf by guest on 28 September 2021 vascular plants in a way that allowed has a hinged cover (Figure 1). [I their understanding of alternation of high school students to connect living obtained these containers from a generations in the primitive vascular organismswith the concept of altemat- catered luncheon that I had plants. ing haploid and diploid growth forms. attended and cleaned them in an Using stereo microscopes, I have However, several years ago, I discov- autoclave before using.] each student find a fem gametophyte ered a way to grow fern gametophytes 3. Keep the container at room tem- when I am discussing the fem life in the classroom so that my introduc- perature and thoroughly wet the cycle (Figure 3) in class. Also, I use a tory biology students could have speci- surfaceof the soil every day using flex camera and project the image of mens in front of them as we discussed a spray bottle. one onto a TV monitor. The heart- this topic. 4. Illuminate the container with shaped fem gametophyte(N) will have Seniorstaking my term-longecology fluorescentgrow-light bulbs on a archegonia (N) producing eggs (N) in elective did a variation of Darwin's 12/12 hour day/night cycle. the notch of the structure (Figure 4), seed bank investigation, as described 5. Check every day and discard while the antheridia (N) will produce in Weiner's (1994) book The Beak of mosses, angiospermsand gymno- sperm (N) down near the tip. Provided the Finch.They collected some topsoil sperms that germinate. cultures are kept moist, within a few from a small patch of woods behind 6. In about a month, the spores of weeks, antheridia will mature and one of the buildings on campus and ferns should germinate and grow release sperm. The sperm will swim put it in empty clear plastic sandwich into small (1-2 mm) heart-shaped to a neighboringarchegonium and fer- containers near a source of light in gametophytes. tilize an egg that will result in a zygote the classroom.The students then iden- 7. A few weeks later, young sporo- (2N) in the archegonium of that tified and removed all plants as they phytes will grow out of the base gametophyte. sprouted, much as Darwin had done of the notch on the gametophytes. The result of that fertilization will while observing that over a period of then grow into a developing fern six months, 537 plants grew out of frond, the sporophyte (2N) generation. three tablespoons of mud that he had Classroom Application My students also collect developed collected from the bank of a nearby fem fronds from the woods, so that pond. The alternation of generations in plants continues to be a topic that we have them on hand as well for Grasses and other pioneer plants observation of larger specimens. Later came up the first but some students find very difficult to during month, grasp, particularly if the teacher has in the season, the sporophytesproduce then, soon after, heart-shaped fern spores (N) by meiosis. On many types gametophytes appeared. I have all of already covered gamete production in like * .. } i e N . N | .....^ '-.. my introductorystudents performthis diploid organisms, humans. Being |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~... same exercise in April, so that by May '''= =' Zi''''''''';1'f'l--. 7-CE;. I can teach this unit to them with the living structures in hand.
Methods 1. Have your students collect 2" of top soil, using a shovel and a pail, from a mixed deciduous forest in early spring.
Chrstopher R. Matlack is chair of the Figure 2 Fern gametophyte (N) with Science Department at PhillipsExeter Figure 1. Ferns germinatingin a clear young sporophytes (2N) growing out Academy, Exeter, NH 03833. plastic sandwich container. of the archegomia F
594 THEAMERICAN BIOLOGY TEACHER, VOLUME 60, NO. 8, OCTOBER1998 Fern Frond ~~~~~~X Sori Meoi
Developing Sporophyte Meiosis
SPOROPHYTEGENERATION (2N)
GAMETOPHYTEGENERATION (N) Spore 0 Egg Archegonia
Fertilization Downloaded from http://online.ucpress.edu/abt/article-pdf/60/8/594/48698/4450556.pdf by guest on 28 September 2021
7Wi 7 74 Gametophyte Sperm Antheridia
Figure 3. Alternation of generations in the fern life cycle. of ferns, the spores are found on the Acknowledgments underside of the fronds in circular, orange structures called "sori." These I thank Frances Ekstrom for editing spores are released into the soil every the manuscript, Jim Ekstrom for help- summer and should be in your wood- ing to produce the photographs of the land soil sample. developing ferns, and Jim Loats for assisting in making the fern life cycle diagram.
References Weiner, J. (1994). The Beak of the Finch. '4~~~~~~~~~~I A Story of Evolution in our Time. New York: Alfred A. Knopf.
Figure 4. Arc-hegoniain the notch of the fern gametophyte.
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GROWINGFERN GAMETOPHYTES 595