Nostoc is a cosmopolitan form. It occurs on damp earth or floating freely in water. In a fruit can or a battery jar, Nostoc is easily kept year after year in the laboratory. Young specimens are generally in the form of gelatinous nodules, but in older specimens the form may be quite various. It is very easy to make sections, since the gelatinous matrix cuts well and holds the filaments together.
Chromoacetic acid is a good fixing agent.
Stains which stain the gelatinous matrix make the preparations look untidy, but they show that each filament of the nodule has its own gelatinous sheath. Small nodules may be stained in bulk and be got into Venetian turpentine. Crushed under the cover, they make instructive preparations.