Study Of Riccia PDF

**STUDY OF RICCIA** **Division - Bryophyta** **Class -- Hepaticae** **Order -- Marchantiales** **Family -- Ricciaceae** **Genus -- *Riccia*** **Gametophyte** *Riccia* is a bryophyte in which the gametophyte is haploid, dominant and independent phase. Gametophyte is dorsiventrally flat thallus...

**STUDY OF RICCIA** **Division - Bryophyta** **Class -- Hepaticae** **Order -- Marchantiales** **Family -- Ricciaceae** **Genus -- *Riccia*** **Gametophyte** *Riccia* is a bryophyte in which the gametophyte is haploid, dominant and independent phase. Gametophyte is dorsiventrally flat thallus, which forms circular patches called rosettes on the moist substratum. Thallus is dichotomously branched. Each thallus lobe shows a dorsal groove or midrib. At the tip there is a notch with a growing point. Thallus is attached to the substratum with the help of root-like rhizoids. Rhizoids are unicellular and smooth walled or tuberculate. Rhizoids are concerned with anchorage and absorption. There are multicellular violet obliquely placed scales which retain moisture. riccia riccia Classification (Systematic position) - - ppt download **V.S. of thallus of *Riccia*** It shows distinct upper photosynthetic and lower storage region. Photosynthetic region is made up of many photosynthetic / assimilatory filaments which lie parallel to each other with air canals in between. Each photosynthetic filament is made up of chlorenchymas cells arranged in a single row. Terminal cell of each filament is globular and hyaline / transparent. All such terminal cells form a discontinuous or ill-defined upper epidermis. Lower storage region is made up of parenchymatous cells which store food material. Sex organs are embedded in the storage region. Lowermost layer of the storage region forms well defined continuous lower epidermis. Unicellular rhizoids and multicellular scales arise from the lower epidermis.  **[Sexual reproduction]** Riccia is homothallic and bears both male and female gametangia in the same thallus. Gametangia are embedded in the storage region. **V.S. of thallus showing antheridia** Antheridia are male gametangia which are produced in the antheridial cavity, embedded in the storage region, just below the dorsal groove. Each antheridium shows a lower stalk and a globular body. The globular body is covered by the sterile jacket which encloses biflagellate motile antherozoids or male gametes. **V.S. of thallus showing archegonia** Archegonia are the female gametangia which are embedded in the storage region, just below the dorsal groove. Each archegonium is a flask shaped structure made up of stalk, venter and neck. Globular venter encloses a small venter canal cell and a large egg cell or non-motile female gamete. Neck is tubular, covered with six rows of neck cells. Neck encloses four neck canal cells. Neck is closed by cap cells / cover cells / lid cells. At maturity, motile male gametes get attracted towards non-motile female gamete by [ ] chemotaxis[.] Fertilization leads to the formation of a diploid zygote, which is the first cell of the sporophytic generation.  **V.S. of thallus showing sporophyte** After sexual reproduction, the gametophytic generation ends and the sporophytic generation starts. Zygote is the first cell of the sporophytic generation. Sporophyte of *Riccia* is the simplest one, made up of only capsule. Foot and seta are absent. Venter forms protective calyptra around the capsule. Capsule is covered by a sterile jacket, which encloses diploid sporocytes or sporemother cells. During asexual reproduction, the sporocytes undergo a reductional division - meiosis to produce four haploid spores each. A maturity when the calyptra disintegrates, the haploid spores are set free. Each spore is triangular, unicellular, uninucleate haploid structure. Each spore is enveloped by two layered wall - outer, thicker, spiny exosporium and inner, thinner, smooth endosporium. Spores germinate to produce a haploid gametophyte of next generation. Riccia - Fertilization, Sporophyte Generation