ABSTRACT
Algae are eucaryotic, unicellular or multicellular organisms and mostly occur in aquatic environments. Algal cells may be spherical, rod shaped, barrel shaped, club shaped or spindle shaped and the size ranges from 1.0 mm to many cm in length. The three kinds of photosynthetic pigments in algae are chlorophylls, carotenoids and biloproteins or phycobilins. The rusty colour of the pustule may be due to presence of orange colour pigment in the sporophore and sterile hairs. The algae produce a disc-like thallus which is multi-layered in the centre and single layered in the periphery. The cells have chlorophyll a, b and carotenoid as photosynthetic pigments and cell wall contains cellulose, xylan, mannan, etc. It grows between the cuticle and epidermis of the host and very rarely between epidermis and palisade cells. Rhizoids arise from the thallus extend to the underlying cells and act as anchoring as well as absorbing organ.
