Marchantia

SYSTEMATIC POSITION

Division : Bryophyta

Class : Hepaticopsida

Order : Marchantiales

Family : Marchantiaceae

Genus : Marchantia

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OCCURENCE�

• The genus Marchantia includes about 65 species distributed all over the world. In India, only 11 species have been reported.
• All the species are terrestrial growing on moist shaddy places, damp soil, moist rocks and banks of streams.
• Common Indian species are : M. polymorpha, M. palmata, M. nepalensis, M. indica, M. simlana

GAMETOPHYTIC GENERATION�

VEGETATIVE STRUCTURE : Dorsal Surface

• prominent mid rib which deepens at the apex
• presence of gemma cups which enclose a number of gemmae
• gemmae are the means of asexual reproduction
• sex organs are borne on special upright branches :
• antheridiophores bear the antheridia whereas archegoniophores bear the archegonia

VEGETATIVE STRUCTURE : Ventral Surface

• shows median grove
• rhizoids and scales are attached
• rhizoids are of two types :

1) Smooth walled (G) : inner walls smooth, living cells, fix the plant body to substratum and absorb water and soil solutes

2) Tuberculate (F,H) : peg like ingrowths in their inner walls, living in the beginning but lack protoplasm at maturity, helps to retain moisture in the ventral surface and carry water to all the absorptive parts

• scales are of two types :

1) Appendiculate (D): large, wedge shaped, bear an appendage at their tips

2) Ligulate (E): simple, small, tounge shaped and without appendage

• scales secrete mucilage and protect the growing

point from desiccation

INTERNAL STRUCTURE

1. Epidermal region : well marked upper and lower epidermis. upper epidermis is interrupted by barrel - shaped air pores. function of air pores is to facilitate gaseous exchange.
2. Photosynthetic Zone : consists of regularly arranged air chambers seprated with each other by septa. a large number of photosynthetic or assimilatory filaments arise from the floor of air chambers. perform the function of photosynthesis.
3. Storage Zone : consists of compact, colourless, thin walled parenchymatous cells which store starch grains and protein bodies. A few cells are filled with mucilage and oil bodies.

REPRODUCTION

• Vegetative Reproduction :

1) Fragmentation

2) Adventitious branches

3) The Gemmae :

- produced inside the gemma cups

- these cups are produced on the dorsal surface of thallus

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• Sexual Reproduction :

- oogamous

- all the species are dioecious

- male sex organs are antheridia and female sex organs are called archegonia.

POSITION OF SEX ORGANS�

• borne on special erect and stalked branches called gametophores or receptacles.
• receptacle bearing antheridia is called antheridiophore and that bearing archegonia is called archigoniophore.
• stalk of both antheridiophores and archegoniophores are morphologically and structurally similar.
• the side corresponding to morphologically dorsal surface of thallus photosynthetic zone.
• the other side of stalk corresponds to the lower ventral side of thallus.

THE ANTHERIDIOPHORE

• differentiated into a long stalk and a terminal disc
• disc is eight lobed
• upper zone of disc consists of air chambers alternating with antheridial chambers
• air chambers possess assimilatory filaments which perform photosynthesis
• antheridia are borne singly inside the antheridial chambers
• antheridia are borne in acropetal succession

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MATURE ANTHERIDIUM�

• differentiated into a short stalk and a large body
• body has single layered sterile jacket
• it encloses a large number of androcytes which metamorphose into antherozoid
• antherozoids are small, uninucleate and biflagellate
• morphologically, antheridia consists of three parts :

1) Head piece : comprising of basal bodies with two long and equal flagella attached to it

2) The nuclear portion : consisting of long narrow rod- shaped and coiled nucleus

3) The cytoplasmic portion : comprising of a thin film of cytoplasm with a few plastids and mitochondria

DEHISCENCE OF ANTHERIDIA

• Dehisce in presence of water provided by rain or dew drops
• at maturity, the pore of antheridial chamber becomes wide open through which water enters and fills the chamber
• the body of antheridium encloses a mass of free antherozoids which float in a viscous fluid formed by dissolution of cell walls of androcytes
• sterile jacket cells imbibe water , become softned, get disorganised
• antherozoids ooze out in mass through an opening
• they escape through the pore of antheridial chamber and come to the surface of disc
• antherozoids swim in the film of water

THE ARCHIGONIOPHORE

• it is the reproductive branch bearing archegonia
• it is differentiated into stalk and disc
• disc consists of eight lobes directed away from the centre
• the archegonia develop on the upper surface of disc in arranged in eight rows
• after fertilization central portion of disc buldges out and becomes convex pushing the archegonia at the periphery
• the archegonia are inverted and hang downward from the tissue of disc
• each archegonium has an extra sheath called perigynium
• each group of archegonia is enclosed within a two lipped, curtain like involucre called perichaetium

STRUCTURE OF MATURE ARCHEGONIUM

• mature archegonium is flask shaped
• it consists of a short few celled stalk, a

globular venter and a long neck

• the apical part of neck is covered by 4

cover cells

• the swollen venter consists of single

layered jacket and encloses a venter

canal cell and a large egg

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SPOROPHYTIC GENERATION

STRUCTURE OF MATURE SPOROGONIUM

• Each sporogonium is differentiated into foot, seta and capsule
• it is enclosed within a protective covering called calyptra
• the other protective coverings are perigynium (pseudoinvolucre) which encloses single sporogonium and perichaetium (involucre) which covers the group of sporogonia

-Foot : it anchors the sporogonium and absorbs water and nutrients from the gametophyte

-Seta : it connects the capsule with foot

-Capsule : it has single layered wall enclosing a mass of spores and elaters. Elaters are hygroscopic and in this way help in spore dispersal

- The sporophytic generation of lifecycle ends with the formation of spores

- The spores are carried away wind or rain

THE YOUNG GAMETOPHYTE

• Spore is the first cell of gametophytic generation
• Spore has thick wall differentiated into outer, thich exine and inner, thin intine
• Each spore mother cell of Marchantia produces 4 spores, out of which 2 develop into male thalli and 2 develop into female thalli
• Thus Marchantia shows physiological heterospory

ALTERNATION OF GENERATIONS

-Since the plant bodies of two generations are morphologically dissimilar, it is called heterologous type of alternation of generations

- and the life cycle is diplohaplontic

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