BSc 1st Year Botany Life Cycle Of Marchantia Notes
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प्रश्न 1 – केवल चित्रों की सहायता से मार्केन्शिया (Marchantia) के जीवन–चक्र (Life – Cycle) को दिखाइए।
मार्केन्शिया का जीवन–चक्र
(Life – Cycle of Marchantia) Notes
life cycle of Marchantia, a liverwort (Familie: Marchantiaceae, phylum: Hepatophyta; sometimes Marchantia is called umbrella liverwort). Like other mosses, Marchantia shows an alternation of generation (more hereabout in mosses). Moreover, Marchantia follows sometimes a vegetative reproductive path by means of gemmae.
The alternation of generation in Marchantia follows the next path (beginning from the haploid spore):
A compact, filamentous protonema with short rhizoids is formed from the haploid spore. A new thallus develops from this protonema by means of mitotic divisions. The male and female gametangia, called respectively antheridia and archegonia, are formed on this young thallus. In each antheridium numerous male gametes (antherozoids = sperms) are produced, but in each archegonium only one large single egg cell is produced (ovum). The sperm cells which are foreseen of flagella can reach the female gametophyte by means of a drop of (rain)water. Through capillary action the water can penetrate into the archegonium and the sperm cells can reach the immobile egg cell and fertilize it (oogamy). The zygote remains in this enclosure and does not pass a rest stage, but it develops inside the archegonium into a sporophyte. The diploid sporophyte grows thus on the gametophyte. Inside the sporangium meiotic divisions occur. The product of these divisions in Marchantia are (haploid) spores. Some diploid cells in the sporangium expand and form elateres (tubular cells with spiral-like thickenings) that contribute to the dissemination of the spores.