TAXONOMY 



229 



tered through the protoplasm. The whole is surrounded by a cell 

 wall which undergoes mucilaginous modification producing thus 

 the- soft gelatinous envelopes which encircle parent-, daughter-, 

 grand-daughter- and even great-grand- 

 daughter-cells. 



Oscillatoria. Oscillatoria is a blue-green 

 filamentous organism found abundantly on 

 the surface of the mud of drains and ditches 

 as well a's in ponds where the water is foul. 

 The filament is slender and composed of 

 compactly arranged disc-shaped cells wh'ch 

 are all alike, excepting the terminal ones 

 which appear rounded off. The filaments 

 tend to be agglomerated in thick felts or 

 gelatinous masses and each possesses pecu- 

 liar oscillating and forward movements. 

 At the time of reproduction the filament 

 breaks up transversely into short segments, 

 each of which, by fission occurring among 

 its cells, grows into a new filament. 



Nostoc. Nostoc occurs on the damp 

 ground bordering streams or in slow bodies 

 of water as greenish or brownish tough gela- 

 tinous masses varying in size from a pea 

 to a hen's egg. When one of these masses 

 is dissected and examined microscopically, 

 it is seen to contain, imbedded in a gela- 

 tinous matrix, numerous serpentine fila- 

 ments, composed of spherical or elliptical 

 cells loosely attached to each other in 

 chain-like fashion. Most of the cells are of 

 the blue-green vegetative kind but there 

 occur at intervals larger cells, often devoid PIG II0 . Nostoc , (h ), a 

 of protoplasm which are termed heterocysts. heterocyst. 



Frequently the filaments break apart on 



either side of the heterocyst, setting free segments of cells which 

 grow into new filaments. 



