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Marchantia jb

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Reproduction of Marchantia

Publié dans : Formation

Marchantia jb

  1. 1. REPRODUCTION IN MARCHANTIA Reproduction: Vegetative: 1. By Fragmentation: 2. Formation of adventitious branches: 3. Formation of Gemmae: Gemmae are multicellular bodies, develop inside gemma cups, on the upper surface of thallus, in midrib region. • They are green, flat, biconvex structures with a short, single celled stalk. • Several cells thick in the middle, deeply notched at the edges. • Meristematic cells present below the notches • Majority cells are green chlorenchymatous. Some cells contain oil- oil cells • Some cells on the surface are colourless- rhizoidal cells – develop into future rhizoids. • Along with gemmae, mucilage cells found in the cup, secrete mucilage which swells and helps in detachment of gemmae. • Gemmae fall on soil and germinate. Rhizoidal cells develop into rhizoids. Meristematic cells of the notch develop into two separate plants. Middle portion decay.Sexual Reproduction: Oogamous type. Thalli are sexually dimorphic or heterothallic, male plants produceantheridiophores and female plants produce archegoniophores at their tips.Structure of Antheridiophore: Consists of a long stalk and a 8-lobed disc-like receptacle at the tip.Antheridia are embedded in the upper surface of each lobe of the disc, in pit-like cavities called antheridialchambers. Alternating with the antheridial chambers, air chambers are present (structure similar to thallus)Antheridia are arranged in acropetal order. Each antheridium is ovoid, with a multicellular stalk. (Structure ofantheridium and spermatozoid similar to that of Riccia).
  2. 2. Structure of Archegoniophore: Consists of along stalk and a 8-lobed disc-like receptacle atthe tip, the lobes of the receptacle benddownwards and inwards. Hanging structurescalled rays develop from the margin of the disc.Archegonia are present on the upper surface ofthe receptacle in young archegoniophore, inacropetal order. They are in median rows oneach lobe.After fertilization, the central part of the discgrows rapidly. As a result, the archegonia arepushed to the lower surface and they become pendulous.Between rows of archegonia, a curtain-like tissue called perichaetium or theinvolucre develops. It is single cell in thickness and fringed in the margins.Structure of Archegonia: Structure is similar to that of Riccia. Only difference isnumber of Neck Canal Cells is 8 (in Riccia 4).Fertilisation: Splash mechanism due to rain drops. Refer Riccia.Structure of Sporophyte: The diploid zygote develops into the sporophyte inside theventer of the archegonium. Mature sporophyte shows three distinct parts: • Foot: The basal, broad, parenchymatous part. Embedded in the tissue of the archegoniophore. Absorptive and anchoring in function. • Seta: It connects the foot and capsule. Consists of many vertical rows of cells. • Capsule: oval, spore producing structure at the apex of the sporophyte. Covered by a single-layer of cells called capsule wall. Many haploid spores or meiospores and sterile elaters are found inside the capsule. • The spores are small globose structures with a spore wall consisting of exine and intine, a single nucleus and little cytoplasm. They germinate into new thalli. • Elaters long ribbon-like multicellular structures. They are hygroscopic and help in spore dispersal. • Mature sporophyte is protected by three coverings – perigynium, calyptra and perichaetium.Dehiscence and spore dispersal: Maturecapsule splits along 4-6 lines. Spores arereleased due to the hygroscopic movementof elaters. Liberated spores germinate intonew thalli, in the presence of water.©Dr. Jayakara Bhandary M.Associate Professor of BotanyGovt. Degree College, Karwar