(i) By cell division: This is only the known method of propagation in the order Chroococcales. The cell becomes constricted in the middle and ultimately divides giving rise to two individuals. (ii) Fragmentation of colony: The colonies are fragmented into small bits. Each such bit develops into a colony by division of the cells in different planes. (iii) Fragmentation of filaments: In the family Oscillatoriaceae the filaments break into small fragments. The fragmentation may be accidental or otherwise. (iv) By hormogones: Inside the sheath, the trichomes are fragmented and hormogonia or hormogones are formed. Each such hormogone or hormogonium may develop into a new individual, e.
g., many Nostocales. (v) Hormospores or hormocysts: During the formation of hormospores, a large quantity of food material is accumulated in the cells of hormogones and they become thick walled, these structures are called the hormospores or hormocysts. Each such structure develops in a new plant on the approach of favourable conditions, e.
g., Westiella. (vi) Akinete formation: Sometimes some of the cells of filamentous genera accumulate much of food, become thick-walled and are called the ‘akinetes’. These are produced in unfavourable conditions; each such vegetative structure may develop into a new filament, e.g., Nostoc. On the approach of favourable conditions the akinetes develop into new filaments; the akinetes are also called the ‘arthrospores or resting spores’.
The asexual reproduction takes place by means of (i) endospores and (ii) exospores. (i) Endospores: The endospores are produced inside the cell. During the formation of these spores the cytoplasm of the cell becomes cleaved into several bits. Thease bits later become endospores and are liberated. Each spore germinates into a new plant, e.g., Dermocapsa. When the endospores are comparatively smaller in size and larger in number in the cell, they are called ‘nannospores’.
Such spores develop individually into new individuals, e.g., Dermocapsa.
(ii) Exospores: Such spores are produced outside the cell by constriction. In the case of Chamaesiphon, the exospores are developed from the terminal end of the plant in continuous succession. The cyanobacterium is epiphytic upon Oedogonium.