The subaerial part is tubular or ovoid, and contains the chloroplast (clil.).
In Spirogyra and allied forms the chloroplast grows as the cell grows, and only divides when this divides.
Sometimes several pyrenoids occur in each chloroplast, as in Mesocarpus and Spirogyra; sometimes only an occasional chloroplast contains pyrenoid at all, as in Cladophora.
The chloroplast consists of two parts, a colorless ground substance, and a green coloring matter, which is contained either in the form of fibrils, or in more or less regular spherical masses, in the colorless ground-mass.
These substances can, however, be dissolved out in water, and the green coloring matter of the chloroplast then becomes visible.