BLUE-GREEN ALGAE 107 



24 (2) Cells epiphytic; with a distinct base and apex. 



Family CHAMAESIPHONACEAE. 

 Only one genus. . . Chamaesiphon A. Braun and Grunow. 



Cells small, ovoid, pyriform, or cylindrical; attached 

 by their base and generally widening upwards to their 

 free apex. Solitary or aggregated; sheaths present; 

 cell walls very thin; cell contents homogeneous, blue- 

 green, violet, or yellow; reproduction by one-celled, 

 non-motile cells which are successively cut off from 

 the upper portion of the plants, gradually escaping 

 from the open apex. Common on Oedogonium and 

 other algae in ponds. 



FIG. 42. Chamaesiphon incrustans Grunow. X 800. 

 (After West.) 



25 (i) Plants filamentous; filaments simple or branched; consisting of 



one or more rows of cells generally enclosed within a more 

 or less evident sheath. Asexual reproduction by means 

 of hormogonia, and more rarely by spores. 



Order Hormogoneae Thuret . . 26 



26 (64) Filaments cylindrical, sometimes narrowed at the extremities. 



Suborder Psilonemateae . . 27 



2 7 (53) Filaments not branched 28 



28 (43) Filaments consisting of a single row of cells, seldom (Spirulina) 



one-celled; not branched; heterocysts absent; sheaths vari- 

 able, more or less gelatinous, and sometimes enclosing more 

 than one filament. . . . Family OSCILLATORIACEAE . . 29 



2 9 (39) Never more than one filament within a sheath. 



Subfamily LYNGBYEAE . . 30 



30 (31) Filaments apparently one-celled, coiled into a regular spiral, often 



showing rapid rotatory movements. . . Spirulina Turpin. 



Filaments very narrow, consisting of a single 

 elongated cell, sometimes of great length, regularly 

 spirally coiled; sometimes showing rapid oscillat- 

 ing and rotatory movements. Common hi stag- 

 nant water. 



FIG. 43. Spirulina major Kiitzing. X 1000. (Orig- 

 inal.) 



31 (30) Filaments many-celled 32 



32 (36) Filaments simple, generally showing oscillating and gliding move- 



ments; sheaths thin, hyaline, sometimes not evident. . 33 



