Oedogonium

Oedogonium is an exclusively fresh water algae. Out of about 400 species more than 200 have been reported from India. They are very common in pools, ponds, lakes etc. The

filamentous plant body may get attached with the stone, wood, leaves of aquatic plants, small branches of dead plant remain in water etc. by their basal cell the holdfast. Some species like O. terrestris are terrestrial.

PLANT BODY

The thalloid plant body is green, multicellur and filamentous. The filaments are unbranched and cells of each filament attached end to end and form uniseriate row. The filament is differentiated into 3types of cells: 1. Basal cell, 2. apical cell, and 3. Middle cells.

Basal cell:

It is the lowermost cell of the filament.th e cell is long, gradually narrowed and towards the basal  end it expands to form simple,  disc-like, multilobed  or finger-shaped Structure. The cell is generally colourless, which performs the function of fixation to the Substratum and called holdfast.

Apical cell:

It is the topmost cell of the filament.  The cell is usually rounded towards apical side and green in colour.

Middle cell:

All the cells in between basal and apical cells are alike. The cells are longer than their breadth i.e., rectangular in shape.                                                                                                                                                                

Towards the upper end of some cells a ring like structure is present known as cap or apical cap cell. The cap is called cap cell. The number of caps on a cell indicates the number of cell divisions in that cell.

CELL STRUCTURE

The intercalary cells are longer than their breadth and are cylindrical in outline. The cells are surrounded by thick and rigid cell wall. The cell wall is a differentiated into three layers:  an outer chitin, middle pectin and innermost cellulosic. Just interior to the wall, cell membrane is present, which encloses the protoplast. The protoplast consists of cytoplasm, chloroplast and nucleus. The cells contain many small or single large vacuoles situated in the centre and remain filled with cell sap. The cytoplasm lies between the cell membrane and vacuole. The chloroplast is single, large and reticulate, which remains embedded in the cytoplasm. It extends from one end of the cell to the other end. Cells are uninucleate and nucleus is generally present in the centre of the cell within the cytoplasm or it may be excentric.

Species

Species of Oedogonium are divided into two major groups on the basis of the distribution of the sex organs:

Macrandous Species

In these species, antheridia are borne on filaments of normal size. This group is further subdivided into:

• Macrandous Monoecious – In these species, antheridia and oogonia are found on the same filament. Eg: O. nodulosum and O. fragile
• Macrandous Dioecious – In these species, antheridia and oogonia are borne on different filaments. Although filaments bearing antheridia and oogonia are morphologically similar, they differ physiologically. Eg: O. crassum and O. aquaticum

Nannandrous Species

In nannandrous species, filaments bearing antheridia and oogonia show morphological distinction. The male filament, which are much smaller than the female filament, is called a dwarf male or nannandrium. Nannandrous species are always dioecious, i.e., antheridia and oogonia are borne on different filaments. The small male filaments are likely to be attached to a female filament, near an oogonium.