Computer enhanced light micrograph of Nostoc, a blue-green algae. Nostoc is a nitrogen-fixing algae which means it converts gaseous nitrogen into an organic form easily absorbed by plants. Innoculation of soils, particularly in rice culture, has greatly improved yields. It is a Filamentous organism forming chains of individual creatures. Aggregations of this algae form mucilaginous masses, which can be seen resting on the soil. Phase contrast. Mag: X`160 (at 35mm size).