- Nostoc
filaments
are made up of spherical or barrel-shaped cells of uniform size
that are blue-green or olive green in color. The bent, kinked,
or coiled filaments are long, isopolar, and held together by
firm mucilage. The colonies may be microscopic or macroscopic,
smooth or warty in
texture, loose or dense, and spherical, flat, gelatinous, or
in irregular mats. Spherical colonies are usually marble-sized,
but may be as large as 30-50 cm in diameter. The mucilaginous
sheaths are firm and wide, yellow, brown, or black in color,
and are most easily viewed in young colonies.
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- The
heterocysts (arrow, top right image) are solitary, barrel-shaped
or spherical, and may be intercalary or located at the ends of
the trichomes. The akinetes are ellipsoidal and only slightly
larger than the vegetative cells. The akinetes of Nostoc
are usually located halfway between the heterocysts. This differs
from Anabaena, where the akinetes are normally adjacent
to the heterocysts.
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