298 THALLOPHYTES 
group pertains to the organization of the cell. In a few of the 
most highly developed forms the protoplast is pretty well organ- 
ized, but in most Blue-green Algae the nucleus and cytoplasm 
are not clearly differentiated and there are no chloroplasts. The 
chlorophyll and other pigments are diffused through the cyto- 
plasm and sometimes throughout the entire protoplast. 
A simple form of Blue-green Algae is Gleocapsa shown in Figure 
255. This plant, which lives mostly on wet rocks, consists of a 
single globular cell with a rather prominent gelatinous sheath 
and is about as simple as a plant can possibly be. By the divi- 
Fig. 255. — Gleocapsa, one of the 
simplest of the Blue-green Algae. A, 
single individual enclosed in a heavy 
gelatinous sheath and beginning to 
divide. B and C show how the 
plants as they multiply are held to- 
gether by the gelatinous sheath. 
>< 540. After Strasburger. 
Fic. 256. — Portions of three fil- 
aments of Oscillatoria. At the left 
one cell in the filament has died, 
resulting in segmenting the fila- 
ment. XX 540. 
sion of the cell new individuals are formed, which are held 
together in loose aggregations by the gelatinous secretion from 
their walls. 
One of the common colonial forms is Oscillatoria, of which there 
are about 100 species (Fig. 256). They form bluish green felt- 
like mats in fresh and salt water, and bluish green layers on moist 
soil. The colony is a filament, consisting of a large number of 
short cylindrical cells joined end to end and enveloped in a thin 
gelatinous sheath. Usually the filaments occur together in large 
numbers, and often there is enough of the gelatinous secretion to 
hold them together in loose aggregations. A characteristic 
feature of the plant, as the name suggests, is the swaying and 
revolving movement of the filament, which sometimes resembles 
