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Common name: Pond silk
Spirogyra is a fresh water free floating green algae. It is commonly found in pond, pool, ditches, lakes and riverbanks. During the rainy season, filament of spirogyra forms green appearance in the stagnant water. The plant body is thallus. Type of thallus is filament which consists of many cells arranged in uniseriate manner i.e. arranged in such a way that one cell appears above another. Each of the filament is elongated, multicellular, cylindrical, unbranched silk-like or thread-like. The filament is covered by mucilage layer which makes plant body slippery and prevents from decaying.
Each of the spirogyra cells is rectangular in shape surrounded by two common layers i.e. cell wall and cell membrane. The cell wall is made up of cellulose, hemicellulose and pectin. It is further differentiated into outer mucilage layer and inner cellulosic layer. The cell membrane is bounded by protoplasmic mass of the cell. Protoplasmic mass of the cell is differentiated into the cytoplasm, nucleus and vacuole. Cytoplasm is in granulated form and lies at the peripheral region. It contains cytoplasmic organelles. In each of the spirogyra cell, chloroplast is ribbon-shaped and spirally arranged. Chloroplast surface contains small rounded protein body is called pyrenoid. It stores starch. Nucleus and vacuoles lie at the central region of the cell. Centrally located vacuole is surrounded by tonoplast. It contains cell sap.
Spirogyra reproduces by vegetative, asexual and sexual methods.
Vegetative reproduction takes place by the process of fragmentation. The breaking process of the entire filament of spirogyra into small individual pieces due to dead and decaying of the intermediate cell is called fragmentation. During unfavourable condition, spirogyra filament break into the small fragment and individual fragment grow independently to form a new filament of spirogyra.
In spirogyra, asexual reproduction takes place by the spore formation.
Akinetes: Akinetes are thick walled, non-motile resting spores and during the unfavourable condition, the protoplasmic mass of the vegetative cell loss water and rounded at the centre. They secrete their own cellulosic cell wall and become thick-walled cells called akinete formation. After releasing from the mother filament, akinetes absorb water and germinate to form a new filament of spirogyra.
Aplanospores: These are thin walled, non-motile spores.
Azygospores: Sometimes when the gametic union does not occur between male and female gametes. These gametes develop spores called azygospore or parthenospore.