Structure of Thallus in Chlorophyceae

Plants of chloroplyceae show variations in vegetative structure from unicellular to multicellular forms. They are as under

(1) Motile Form:- In the organization of thallus these forms of algae are simplest. They are unicellular and remain motile. e.g. ehlamydomonas in green algae. This is spherical, unicellular, unimucleate and biflagellate structure with cup-shaped chloroplast. The cells swim with the help of flagella.

Motile unicellular algae from celonies which move about in the water with the help of flagella of peripheral cells. Each colony has a definite number of cells arranged in a specific manner e.g. volvox

(2) Palmelloid forms:- Palmella stage is a temporary phase in life history of many algae e.g. chlamydomonas but in certain member of chlorophyceae xanthophyceae, chrysophyceae, this state of existence becomes permanent. Plant body remains embedded in a common gelatinous matrix of reproduction e.g.: sphaerocystis.
FIG 1-C PAGE 16 ALGAE BY G.L. CHOPRA

(3) Cocoid forms: In members of order chlorococcales small nonmotile cells are held together to form non-motile colonies with either a definite of indefinite number of cells. They are free-floating colonies e.g. Pediastrum and Hydrodictyon.

(4) Filamentous forms: Some algae have thread-like plant body. These threads are called filament. Filamentous forms are derived either from palmellate or unicellular motile forms. They contain filaments which are composed of several cells placed one above the other e.g. ulothrix, spirogyra and ordogonium. This is called branched filamentous habit. Sometimes filaments may be branched e.g. cladophora. This is known as branched filamentous habit.

(5) Heterotrichous forms: This type of thallus met within the chartophorals among green algae. It has prostrate creeping system and an erect projecting system. Both systems are present in stigeocloneum while in others one of these systems is present and the other is less developed, reduced or completely suppressed e.g. Coleochaete, Draparnaldiopsis.

(6) Siphonaceous forms: The here unicellular body of the plant is enlarged to form a nonseparate multinucleate sac. Protosiphon has un-separate, un-branched tubular thallus containing nuclei. In vaucheria thallus is branched and contains numerous nuclei. In Caulerpa there is a complex development of coenocytic branches to form a thallus which may be 10 cm in height with definite external forms.

(7) Complex forms: In chara plant body is highly developed. Plant remains attached to the soil by rhizoids. These branches are of limited and unlimited growth, former bearing sex cells. The plant looks like an Angiosperm. This indicates that there is an evolution of the vegetative form of unicellular to multi-cellular complex forms.

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