TAMRALIPTA MAHAVIDYALAYA SUB: BOTANY TOPIC:

Gametophytic plant body: Dichotomously branched, prostrate, dorsiventrally flattened thalloid structure.
Midrib present on the upper surface of the thallus.
Presence of apical notch or growing point i.e. the groing part of the thallus.
Ventral surface bears scales that protect the growing point of the thallus from desiccation and unicellular rhizoids (smooth walled and tuberculated) that absorbs the water and nutrients from soil.
The dorsal surface bears antheriodiophore with antheridium and archegioniophore with arechegonium. External structure: Fig.2: A. Male and B. Female plant of Marchantia polymorpha. A B<br>

Internal structure: Internaly Marchantia thallus contain two regions- Photosynthetic and Storage region.
Upper dorsal epidermis contain chloroplasts. Air chember is present on the upper epidermis. Chloroplast containg simple or branched filaments aries from the floor of the air chember that connects with atmosphere through air pores.
Lower epidermis bears unicellular rhizoid and multicellular scales.
storage region present just below the air chembers that contain thin walled parenchyma cells without chloroplast.The cells of storage region contain starch or protein granules or oil or mucilage. Fig.3: A. Internal str. Of thallus, B. Single scale, C Smooth D. Tuberculated rhizoid A B C D<br>

REPRODUCTION: Marchantia reproduces both vegetative and sexually. Vegetative Reproduction: 1. By adventitious branches: Adventitious branches aries from the ventral side of the thallus or reproductive buds. The branches separate from the parent thallus and grow into new thallus. 2. By progressive death: When progressive death and decay of the thallus reaches dichotomy, the two lobe separates and each separation lobe froms new thallus. 3. By gammae: gammae are the specialised asexual multicellular bodies present within the cup shaped structure called gemma cup that is present in the dorsal surface of the thallus. Mature gammae release from the gemma cup, germinates and form a new thallus. Fig.4: A. Adventitious branches, B. Progressive death of the thallus, C. Gemma cup and gammae. A B C<br>

B. Sexual Reproduction: Marchantia is dioecious or heterothallic that means male sex organ antheridium and female sex organ archegonium develope on separate plants. Antheridiophore is a stalk bearing at its appex a convex disc shaped structure. Numerous antheridium develop in a acropetal manner with in the disc.
Each antheridia present within a chember like structure called antheridial chembes. A mature antheridium has a short stalk and a globular body covered by jacket which encloses a number of sperm mother cells. A single sperm mother cell forms two androcytes, each of which develops a biciliated sperm or antherozoid. Fig.5: A. Antheridiophore with antheridium, B. Single Antheridium, C . sperm A C B A. Antheridiophore and antheridia:<br>

B. Archegoniophore and archegonia: The archegoniophore is comprised of a stalk and a disc that bears 9 rays. About 12-14 archegonia are arranged in a single row on each ray of the disc.
A mature archegonium is a pendulous flask-shaped structure with a short stalk, which attaches to the lower (ventral) surface of the archegonial disc. A single archegonium has a basal swollen venter containing an egg cell, a ventral canal cell and a row of neck canal cells inside the elongated neck. Fig.6: A. Archegonium with archegoniophore, B. Archegonium A B<br>

Fertilisation of Archegonium: The fertilisation of Marchantia is dependent upon the presence of water. The neck canel cells and ventral canal cell of archegonia disintegrate to form a mucilaginous mass. The mucilage imbibes water, swells and carries the sperm to the egg of the archegonia. The fertilised egg enlarges in size and form the oospore or zygote which is the mother cell of the sporophytic generation.<br>

Structure of the Mature Sporophyte: The mature sporophyte of Marchantia is differentiated into three parts — foot, seta and capsule.
(a) Foot: It is an expanded bulbous mass of cells at the base of the sporogonium, serves as an absorbing and anchoring organ. It absorbs nutrients from the gametophyte.
(b) Seta: It is a slightly elongated stalk that connects the foot to the capsule. The cells are parenchymatous and elongated lengthwise. Thus, seta increases in length and pushes the mature capsule out of the calyptra.
(c) Capsule: It is a yellow-coloured spherical structure, contains numerous spores and elaters. The capsule is protected by three coverings viz. Calyptra, perigynium and perichaetium. Fig.7: Mature Sporophytic plant body<br>

The jacket of the hanging mature sporogonium (capsule) gets dried and splits longitudinally into a variable number of longitudinal lobes. These lobes extend from the apex to the middle of the capsule. The discharge and dispersal of sport to the air are assisted by the coiling and uncoiling of the elaters due to their hygro­scopic nature.
The spores are almost rounded and are very minute in size with a thin inner intine and a slightly thicker outer exine. In some species an additional layer called perispore is also found outside the exine. Dehiscence of the Capsule: Spore is the first cell of the gametophyte which germinates to form a new gametophytic plant body. Marchantia is a dioecious plant. Out of each spore tetrad two spores grow into two male plants and the two into female plants. Fig.8: Stages of germination of Marchantia spores. The new Gametophytic plant:<br>

Alternation of Generation: Marchantia shows gametophytic(n) and sporophytic (2n) generation in their life cycle. The gametophtic generation turns into sprophytic generation through fertilization and sporophytic into gametophytic generation through meiosis Fig.9: Alternation of generation.<br>

REFERENCES: 1. A Text Book of Botany(Vol-I)-Hait.
2. Archegoniates- Baman chandra acharya.<br>

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