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 as 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. —rNostoc 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 Fig 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. 
