THE FILAMENTOUS BLUE-GREEN ALG^ 175 



daughter, granddaughter, and even great-granddaughter cells 

 may remain inclosed in the envelope of the original mother cell, 

 which becomes very much swollen and jelly-like. The outer 

 walls of the groups of cells finally become changed to a soft 

 mucilage, so that the groups of Glosocapsa cells form at times 

 slimy, dark green patches over damp earth, rocks, and logs. 

 The individual protoplasts have an exceedingly simple structure, 

 for the coloring matter is uniformly distributed through the 

 cells and no nucleus can be seen. 



Clathrocystis and Codosphcerium are free, floating cell colonies, 

 often forming greenish scums during the summer months on 

 the surface of park ponds, reservoirs, and other small bodies of 

 water. The colonies of Calosphcerium are spherical, while those 

 of Clathrocystis (Fig. 173, B) become irregular in shape through 

 the development of holes, so that the structure is somewhat 

 net-like. 



209. The filamentous blue-green algae. These frequently 

 form felted or tufted growths or gelatinous expansions of con- 

 siderable size. There are a number of complex branching types, 

 but the following are good examples of the assemblage. 



Oscillatoria is the most interesting type of the Cyanophycece 

 if only one form can be studied. The filaments are generally 

 made up of flattened disk-shaped cells, placed face to face within 

 an exceedingly delicate sheath, much like a roll of coins wrapped 

 in paper. Cell division takes place in all portions of the fila- 

 ment, and several stages are illustrated in Fig. 174, .4. Growth 

 is therefore not confined to the tip or any other special region 

 of the plant. New filaments arise by the breaking apart of the 

 older ones, generally at some point where one or more cells have 

 died (Fig. 174, A, d). The end cells of filaments or fragments of 

 filaments are always rounded, illustrating beautifully the phe- 

 nomenon of cell turgor or pressure from within the protoplast 

 upon the cell membrane. The cell structure of Oscillatoria is 

 very typical of the blue-green algse. The blue-green pigment 

 gives color to the entire outer region of the protoplast, which 



