what are the methods of asexual reproduction in nostoc?

Nostoc reproduces vegetatively by fragmentation and asexually by spores called akinetes.

Fragmentation: The filament breaks up into small fragments at the junction of the heterocyst which further grow into individual filament by cell division.

Akinetes are vegetative cells of the filament that become enlarged and thick walled during some unfavourable conditions and contain reserve food which later germinate into filaments when favourable conditions arise.