Botany - B.Ye. Yakubenko 2017

Part Three. Plant Kingdom (Planthae)
Chapter VII. Systematics of Higher Plants
Laboratory Class Topic 11.30. Class Liverworts (Marchantiopsida)

General Remarks. Liverworts occupy a prominent place in the vegetation Structure of Ukraine. These organisms belong to higher plants, but their body is not yet differentiated into vegetative Organs. The vegetative body is represented by a thallus that branches dichotomously. A central midrib is visible on the upper surface, and growing points are located in the notches of the growing thalli. Due to the division of their Cells, antheridiophores are formed in male thalli, and archegoniophores in female ones. The organs of sexual reproduction are multicellular antheridia and archegonia. Vegetative Reproduction occurs via gemmae and, rarely, through vegetative fragments.

Object: common liverwort (Marchantia polymorpha L.)

Tasks:

1. Examine and draw The structure of the Marchantia thallus.

2. Examine and study the STRUCTURE OF THE sexual organs of Marchantia.

3. Examine and draw the structure of the sporogonium.

Equipment and Materials: herbarium specimens of male and female gametophytes of Marchantia; permanent preparations of sections of male and female receptacles of the sporogonium; Microscope, magnifying Glass, charts.

Macroscopic studies of liverworts. Using herbarium specimens, study and draw the External structure of the thalli of female and male gametophytes of Marchantia (Fig. 84). Its body appears as a green lobed plate with uneven edges. The lower side of the thallus bears numerous simple and ligulate rhizoids. Among them, in each lobe of the thallus, especially near the margin, tiny scales knownamphigastria are visible, which researchers consider to be rudimentary leaves. The Marchantia thallus is dioecious. One thallus bears female receptacles shaped like a deeply lobed disc (with 8–9 rays), with archegonia located on the underside; the other thallus bears male receptacles shaped like a wavy, weakly lobed disc, in the surface cavities of which antheridia are located. Gemma cups are present On the surface of the thalli, containing gemmae with numerous paraphyses that protect them from desiccation.

Having examined the Marchantia thalli, draw their structure and label the male and female receptacles, simple and ligulate rhizoids, gemma cups, gemmae, midrib, growing points, dichotomous branching of the thallus, amphigastria, and sporogonium.

Microscopic Study of the slide. On a permanent preparation of a Cytology/practical/54.html">Longitudinal section of a female receptacle, examine the archegonia of Marchantia. They are arranged in a row beneath the rays of the disc. It is easy to observe that the archegonia in a row are at different stages of maturity: the developed and mature ones lie closest to the margin, while the younger ones are closer to the stalk of the receptacle. Archegonia are flask-shaped and consist of a stalk, a venter, and a neck. The walls of mature archegonia are composed of a single layer of rectangular cells. The lower part of the enlarged archegonium forms the venter, inside of which, occupying the entire cavity, lies the egg Cell with granular contents and a clearly visible Nucleus. Above the egg cell lies another cell, the ventral canal cell. The narrowed part of the archegonium, the neck, is filled with four cells. After examining the section through the female receptacle of Marchantia, make a drawing showing the rays of the receptacle, archegonia with egg cells, and the perianth (Fig. 85).

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Figure 84. Diagram of The life cycle of Marchantia

Using the prepared slide of a cross section through a male receptacle, study the structure of the antheridia. The male disc has a more massive stalk, and its apex is rounded and not divided into lobes. Antheridia are located in separate cavities of the disc. They sit on short stalks, have a single-layered wall, and contain spermatogenic cells that give rise to a tetrad of haploid spermatozoa. Having examined the preparation, make a drawing indicating the stalk of the receptacle, the antheridial chamber, and the antheridium (Fig. 85).

Figure 85. Male and female receptacles of Marchantia

On the prepared slide of the Marchantia sporogonium, study its structure. Under low magnification of the microscope, it can be seen that the sporogonium consists of a FOOT, a cylindrical stalk, and an almost spherical capsule that opens with Teeth (see Fig. 84). Inside the capsule are spores and tiny spiral spring-like structures called elaters. The wall of the sporogonium is single-layered, with characteristic thickening rings in The Cell walls, and opens with teeth. After studying the preparation, draw the capsule of the sporogonium, indicating the foot, stalk, capsule, teeth, spores, elaters, and perianth in the drawing.

Conclusions. 1. Liverworts have a vegetative body in the form of a thallus.

2. These are dioecious plants: some of them form male gametophytes, while others form female ones.

3. The multicellular organs of sexual reproduction are archegonia and antheridia.

Self-Control Questions

1. On The basis of what features are liverworts classified as higher plants?

2. Which plants are called dioecious?

3. Describe the Structural Features of the antheridium.

4. Describe the structural Features of the archegonium.

5. Explain the structural differences between the male and female gametophytes of Marchantia.

6. What are amphigastria and how do they differ from rhizoids?

7. What do you know about the sporogonium, and what is The Role of the sporophyte phase in the Life Cycle of liverworts?