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. 

 X 540. After Strasburger. 



Fig. 256. — Portions of three fil- 

 aments of Oscillatoria. At the left 

 one cell in the filament has died, 

 resulting in segmenting the fila- 

 ment. X 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 



