NOSTOC

Habitat and Occurrence:

It is widely distributed in alkaline soils and on most rocks and cliffs.

Nostoc makes a jelly-like mass in which numerous filaments are embedded.

Structure:

Trichomes are unbranched and appear beaded.

Individual cells are mostly spherical but sometimes appear barrel-shaped or cylindrical. All cells in trichomes are mostly similar in structure but at intervals are found slightly large, light yellowish thick-walled cells called heterocysts.

Trichomes mostly break near heterocysts and form hormogonia thus helping in fragmentation.

Reproduction:

There is no sexual reproduction but it reproduces asexually by the formation of hormogonia.

Hormogonia are formed when filaments break at different points into smaller pieces.

This is due to the death and decay of an ordinary cell or the Heterocyst may serve as the breaking point.

Reproduction can also be due to akinetes formation:

Akinetes are thick-walled, enlarged vegetative cells that accumulate food and become resting cells. On arrival of favorable conditions, they form normal vegetative cells and other body parts.