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| Spirogyra |
Occurrence:
This is very common free floating fresh water alga found in fresh water pools, lakes, etc. in abundance. This is also known as 'pond silk' Or 'water silly. The filaments are slimy in nature because of the presence of mucilaginous substance around them.
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| Spirogyra occurance |
External features and cell structure:
1) The filaments are unbranched and consist of the cylindrical cells arranged end to end.
2) The cell wall of the filament is usually two layered . The outermost layer consists of pectic substances and the layer just outside the protoplast consists of cellulose.
3) Each cell is cylindrical and several times longer than it's breath.
4) The cells are uni-nucleate. The nucleus is usually situated in the centre of the cell and connected by cytoplasmic stands to the dense cytoplasm of the peripheral region.
5) There is a big central vacuole.
6) The chloroplasts are spiral and band like. They may be serrated or smooth at their margins,
7) The number of chloroplasts ranges from 1-14 in different species.
8) Many pyrenoids are found in each ribbon-like chloroplast.
Spirogyra Reproduction:
Vegetative: by fragmentation.
A) Sexual reproduction:
1) Sexual reproduction takes place by special gametes called 'aplanogametes'.
2) Sexual process is known as 'aplano-gamy'.
3) Motile gametes ar always lacking.
4) Aplanogamy takes place by conjugation, which may be 'scalarification' Or 'lateral'.
5) In each cell a single aplanogamete is produced which moves in the other cell through a conjugation tube in amoeboid fashion.
6) The species may be homothallic or heterothallic.
7) Lateral conjugation takes place in homothallic species.
8) In scalariform conjugation the aplano-gametes of two filaments unite whereas in lateral conjugation the aplano-gametes of two adjacent cells of the same filament unite.
Scalariforn Conjugation:
1) This is found in most of species.
2) Two filaments taking part in conjugation lie side by side.
3) The outgrowths are given out from the lateral walls of the opposite cells of the filaments.
4) The outgrowths of opposite cells touch each other, the wall of the contact dissolves and a tubular passage is formed.
5) This tubular passage is called 'conjugation tube'.
6)A single aplanogamete develops in each cell.
7) The aplano-gametes formed in the cells of one filament pass into the opposite cells of the other filament through conjugation tubes in amoeboid fashion.
8) The transfering aplano-gametes are considered male gametes and the receiving aplano-gametes are female filament.
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| Scaliform conjunction |
Lateral conjugation:
1) This type of conjugation is found occasionally and in homothallic species.
2) Here the aplano-gametes of the adjacent cells of the same filament unite.
3) At the septum a tube like structure develops and through this opening the contents of one cell pass into the other.
4) The empty cells are considered as male gametangia and the cells with zygotes as female gametangia.
5) The zygotes are found in alternate cells.
6) The zygote is dark-coloured and thick walled.
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| Lateral conjunction |
Identification and Systematic position:
Sub-Kingdom: Algae
1) Chlorophyll bearing organisms.
2) Unicelluar sex organs of multicellular ones in which every cell forms a gamete.
3) Autotropic in nutrition.
4) Cellulose cell wall
Division and class: chlorophyta
1) Chlorophyll present within chloroplasts.
2) Photosynthetic food product is starch.
3) Usually pyrenoids present within chloroplasts.
Order: conjugales
1) Exclusively fresh water forms.
2) The forms are unicellular or multicellular filamentous. In filamentous forms the cells are arranged end to end.
3) The filaments are unbranched.
4) The chioroplasts may be spiral, axial, or stellate ribbon shaped.
5) Sexual reproduction takes place by means of aplanogametes. Motile gametes absent.
6) Union of gametes takes place by conjugation through conjugation tubes.
Family : Zygnemataceae
1) Unbranched filaments.
2) Uninucleate cylindrical cells. The cells contains either one to several spiral ribbon-like chloroplasts, or a single axial laminate chloroplast, or two stellate axial chloroplasts.
3) Sexual reproduction by conjugation.
Genus: Spirogyra
1) The cell contains one to several spiral ribbon-like chloroplasts.
2) Sexual reproduction by conjugation of aplano-gametes.