Botany - B.Ye. Yakubenko 2017

Part Three. Kingdom Plantae
Chapter VII. Systematics of Higher Plants
Laboratory Session Topic 12.35. Class Ferns, or Polypodiopsida — Роlyроdioрsida. Subclass Salviniidae (heterosporous) ferns &ndash Salviniidae

General Remarks. Heterosporous ferns are rarely found in the flora of Ukraine. They typically inhabit Water bodies or excessively moist depressions. Their key features include: the presence of Two Types of spores—microspores and megaspores; The formation of sporocarps containing micro- and megasporangia developing on a central receptacle; the overwintering of sporocarps at the bottom of water bodies followed by their floating to the surface as gases accumulate between their walls; and a significant reduction of the male and female gametophytes. The sporophyte is dominant in The life cycle of heterosporous ferns, whereas unisexual gametophytes (male and female) play a minor role.

Object: order — Salviniales (Sаlіviniales), representative — water fern

floating (Sаlvinia natans (L.) Аll.)

Task:

1. Study the general Structure OF THE water fern Salvinia.

2. Examine The structure of micro- and megassori using self-prepared slides.

3. Draw the sporophyte, micro- and megassori of Salvinia.

Equipment and Materials: MBR-1 or Biolam microscopes, magnifiers, scalpels, tweezers, live and herbarium specimens, and other supplies.

Macroscopic study of floating Salvinia. Floating Salvinia is a plant that grows in quiet backwaters of large and small rivers, and is frequently cultivated in aquariums. Let us examine its external structure. On the horizontal stem of Salvinia, three leaves are arranged in whorls: two identical green, floating leaves and one modified, dissected into segments, submerged brown leaf (Fig. 93). Salvinia does not develop true roots; their function is performed by the submerged leaf. When examining the leaves under a magnifying Glass, it is evident that their upper surface is covered with relatively tall outgrowths that trap a layer of air, giving the leaves a silvery sheen. The submerged leaf is divided into narrow thread-like segments, which are also covered with hairs. Spherical sori, about the size of a pea, are visible near the Base of the submerged leaf. Draw the general appearance of the floating Salvinia sporophyte, indicating the submerged leaf, floating leaves, and sori on your drawing.

Method for preparing a transverse section of a Salvinia sorus. Take a glass slide and coverslip and clean them thoroughly. Place the glass slide across a pencil case and apply a drop of water to it. Take a Salvinia plant and locate the sori among the modified filamentous brown leaves. Cut them off from the stem and place them into a slit previously made in an elderberry pith. Slice The surface of the pith containing the sori so that the cut passes through the middle of the sorus. Prepare a series of sections in this manner and place the best ones into the drop of water on the slide. Cover them with a coverslip and secure the slide on the Microscope stage with clips.

Microscopic Study of the sori slide. Locate the two types of sori on your prepared slide. In the microsori, you will find numerous microsporangia on long stalks attached to the Placenta. All of them are covered by two walls separated from each other, fusing only at the apex. In the megasori, larger sporangia are visible, attached to the placenta by short, transparent stalks; these are the megasporangia. They are also surrounded by a special envelope, or indusium, which develops on the Short Branches of the lower leaves. Note that the sporangia possess only a single-layered wall and lack a ring of thickened Cells.

Draw the structure of the sori in your workbook and label the indicated parts.

Conclusion. Heterosporous ferns continue the evolutionary Lineage that first emerged in quillworts (Isoetaceae) and became fully established in gymnosperms. Heterospory led to The Emergence of a heavily reduced sexual generation and cross-Fertilization, which promoted The Development of diverse offspring, increased their viability, and provided raw material for further evolution.

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Figure 93 Life Cycle of floating Salvinia:

a — sporophyte; b — sori; c — microsporangium with male gametophyte; d — final stage of male gametophyte development; e — megasporangium; f — megasporangium with female gametophyte; g — megasporangium with sporophyte embryo; h — young sporophyte; 1 — sorus; 2 — submerged leaf; 3 — floating leaf; 4 — stem; 5 — microsorus with microsporangia; 6 — megasorus with megasporangia; 7 — placenta; 8 — megaspore; 9 — archegonium; 10 — gametophyte; 11 — sporophyte embryo

Self-Assessment Questions

1. What vegetative Organs develop in Salvinia?

2. How many types of spores develop in floating Salvinia?

3. How many megaspores are contained in a mature megasporangium?

4. How many spores develop in a microsporangium?

5. What develops from the zygote?

6. Where do microspores develop, and what grows out of them?

7. Name the Structural components of micro- and megasporangiosori.

8. Describe The sequence of developmental stages in the life cycle of water fern (Salvinia natans).