Botany - B.E. Yakubenko 2017

Part Three. The Plant Kingdom (Planthae)
Chapter VII. Systematics of Higher Plants
Laboratory Class Topic 12.34. Class Ferns, or Polypodiopsids (Polypodiopsida). Subclass Polypodiidae, or Isosporous Ferns (Polypodiales)

Modern ferns are known to appear in the Carboniferous period. They are mostly perennial plants: tree-like forms are found in the tropics, while in temperate climates they are herbaceous plants with a subterranean stem—a rhizome—and diverse leaves that are circinately coiled in the bud stage. They are homosporous, less commonly heterosporous plants. Sporangia are gathered into sori and possess an annulus for dehiscence. Gametophytes are terrestrial and green: bisexual in homosporous ferns, and unisexual, dioecious, and reduced in heterosporous ones.

Modern ferns include three groups of orders: Polypodiales, Marsileales, and Salviniales. Among the contemporary flora, including that of Ukraine, the Polypodiales are the most widespread. These are modern homosporous ferns, which include many ornamental species.

The Marsileales and Salviniales are less common in the flora of Ukraine. These are aquatic heterosporous plants that produce Two Types of spores—microspores and megaspores.

Object: order — Polypodiales, representative — male fern (Dryopteris filix-mas (L.) Schott.)

Task: 1. Study and draw the general appearance of the sporophyte of the male fern.

2. Examine a pinna (frond segment) with sori under reflected light.

3. Study the Water/140.html">Anatomical Structure of a cross-section of a pinna segment with sori.

4. Study and draw The structure of the prothallium of the male fern.

Equipment and Materials: MBR-1 or Biolam microscopes, magnifiers, herbarium fern material, slides, other accessories.

Macroscopic Study of the sporophyte of the male fern. Examine the general STRUCTURE OF THE male fern sporophyte using herbarium or living material. Pay attention to the sturdy, woody rhizome bearing a cluster of large bipinnate leaves—fronds. Numerous adventitious roots extend downwards from the rhizome. Draw the general appearance of the plant and indicate the rhizome, adventitious roots, and stem-derived leaves—fronds (Fig. 92). In some specimens, find young leaves and verify that they are circinately coiled.

Macroscopic study of a frond segment with sori. Using a magnifier or under low Microscope magnification, carefully examine the pinnae (segments) of the frond and find the network of Veins on the underside. Pay attention to the regular arrangement of sori relative to the midvein of the secondary pinna segment. The sori themselves are brownish in color. Above, they are covered by a transparent, specific-shaped indusium (Kidney-shaped in our case). Upon closer inspection, you will see numerous sporangia emerging from beneath the indusium, featuring a ring of brown thickened Cells known as the annulus. Draw a leaf segment and indicate on the drawing the sorus, indusium, sporangium, and the venation of the frond segment.

Method for preparing a cross-section slide of a fern sorus. You can use either a ready-made slide or one prepared by yourself. To make a slide, take a Glass slide and a coverslip and clean them thoroughly. Place the glass slide across a pencil case and apply a drop of water to it. Then, take a piece of elderberry pith and make a longitudinal cut 1.5–2 cm deep in it. Insert a small piece of the cut frond with sori into this slit and clamp the pith.

Level the surface and make a few trial sections. Afterward, produce a series of thin sections. Using a magnifier or low microscope magnification, select a few of the best sections among them and place them in the drop of water. A mandatory condition for the slide is that the section must pass through a sorus. Cover the object with a coverslip. Remove excess water using filter paper. Secure the slide with stage clips.

Microscopic study of the sorus slide. Using low and high microscope magnification, study the cross-section slide through the sorus. Draw its structure in your album. On the slide, you can see that the section also passes through the leaf blade. In it, you can distinguish the upper and lower epidermis and the mesophyll located between them. The sorus extends or proliferates from the lower epidermis. It features a prominent lower swollen part called the Placenta. Numerous sporangia on long, thin stalks, which you saw during the macroscopic study, are attached to it. In the middle, rising from the placenta, is a short, multi-layered stalk that expands at the apex into a transparent indusium. It is the indusium that covers and protects the sporangia, especially when young.

Examine and draw the sporangium separately at a larger scale. Extending from the placenta on long, curved, cylindrical stalks are sporangia composed of 2–3 rows of colorless cells. All these sporangia are biconvex, rounded, with a mechanical Cell ring running across their middle. You will easily recognize it by the thickening pattern of The Cell walls: the radial and inner tangential walls are thickened, while the outer tangential wall remains unthickened. The mechanical ring, or annulus, is discontinuous.

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Figure 92. Developmental cycle of the male fern:

a — sporophyte; b — part of a frond with sori; c — cross-section of a frond with sori; d — sporangia; e — spore; f — protonema; g — prothallium (gametophyte);

h — antheridium; i — archegonium; j — young sporophyte; 1 — placenta; 2 — indusium;

3 — sporangium; 4 — sporangium stalk; 5 — thickening ring; 6 — rhizoids;

7 — antheridia; 8 - archegonium

and

Part of the sporangium is not covered by the mechanical ring. This is the thin-walled section of the annular region, called the stomium. It is precisely at this point that the sporangium ruptures and opens. Spores are shed through the resulting rupture. Having finished studying the cross-section of the frond segment with sori, indicate on your drawing: upper and lower epidermis, mesophyll, placenta, indusium, sporangium, annulus, stomium, stalk, sporangium body, and spores.

Microscopic study of the fern prothallium slide. On a prepared slide of the male fern prothallium, carefully examine its structure first under low and then under high microscope magnification. The prothallium appears as a Heart-shaped plate smaller than a coin. The central part of the prothallium is multi-layered, while towards the edges it thins down to 1–2 cell layers. Numerous rhizoids extend from the lower side, by which it attaches to the substrate. Among the rhizoids, pouch-like antheridia with a more intense coloration are visible. In the upper part, closer to the notch, archegonia are embedded in the multicellular tissue, with the tiny necks of the archegonia protruding outward. Draw the prothallium at a larger scale and label the named constituent parts on your drawing.

Conclusion. Modern ferns are mostly perennial herbaceous plants with a stem, adventitious roots, and telome-derived leaves. Spores usually form in sporangia gathered into sori. Gametophytes are bisexual, chlorophyllous, and annual.

Self-Control Questions

1. What classes are Pteridophytes divided into?

2. Where are spores formed in the male fern?

3. Name the constituent PARTS OF THE sorus and sporangium.

4. From what does the gametophyte develop, and what is its structure?

5. Name the MAIN STAGES OF The life cycle of the male fern.

6. Name the constituent parts of the sporophyte and the gametophyte separately.

7. What do sporangia attach to within the sorus?

8. What facilitates the opening of the sporangium and the shedding of spores?

9. Is a liquid-drop medium required for the Fertilization process?