Cholorophycae - Volvocales

Phylum Thallophyta - The Algae - Cholorophacae - Volvocales 
The Volvocales are Chlorophyceae in which the thallus is unicellular or colonial, and is generally motile throughout life. In the colonial forms arate cells may be embedded in a common envelope of mucilage, and the 3 may be systematically linked together by fine protoplasmic threads. The vegetative cells possess extremely fine thread-like flagella, which project though the wall of the cell and are capable of active motion. In the Volvo each cell is generally provided with a pair of flagella of equal length, attached to the anterior end of the cell. They are frequently retracted or shed during periods of rest. Asexual reproduction takes place by the forma­tion of zoospores. l\Iost genera also reproduce sexually, and the simpler members are isogamous. The cell is generally bounded by a cell wall, which may either be delicate or firm and rigid. In the latter case it consists of cellulose. There is usually a single chloroplast situated at the posterior end of the cell and containing a single pyrenoid, or starch-forming centre. There is a central nucleus and one, or more commonly two, contractile vacuoles, which show a rhythmical alternation of rapid contraction (systole) and slow expansion (diastole). They are apparently excretory organs, and in certain forms are known to contain uric acid.
Chlamydomonas, Haematococcus, Gonium, Pandorina, Eudorina, Volvox

Posted in Botany