(1) Motile Form:- In organisation 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 water with the help of flagella of peripheral cells. Each colony has definite number of cells arranged in 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 non motile 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 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: Here unicellular body of plant is enlarged to from a non separate 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 as 10 cms in height with definite external forms.
(7) Complex forms: In chara plant body is highly developed. Plant remains attached to soil by rhizoids. These branches are of limited and unlimited growth, former bearing sex cells. Plant looks like Angiosperm. This indicates that there is evolution of vegetative form of unicellular to multi-cellular complex forms.
