i. Colonies more or less spherical, or formed like a bunch of grapes 



(figs. 8, 9). Microcystis. 



ii. Colonies spherical when 3'oung, torn and net-like when older. 



Clathrocystis. 



hh. Cells wedge shaped ; colonies spherical. Gomphosphcera. 



gg. Cell division two plane, resulting colonies therefore only one 



cell deep. 



h. Colonies a hollow sphere (fig. 10). 



hh. Colonies sheet like or disc like. 



i. Individual cells isodiametric, not flat. 



j. Cells spherical, regularly arranged, (fig. 6). 



jj. Cells cylindrical, arranged palisade like. 



ii. Cells flattened, disc like (fig. 2). 



ff. Colonies attached. 



cc. Multiplication by conidia. Epiphytes on algae. CHAM^SiPHONACE.ii;. 



bb. Cells (except Spirulina, fig. 12) filamentous; branched or unbranched, 



multiplication by filamentous active hormogones. 



HORMOGONE-^. 



Ccvlosphccriu in . 



Merisntopedia . 



Holopedium. 



Tetrapedia. 



Oncobyrsa. 



0000 

 0000 

 0000 

 0000 



6 



^^l^^ 10 



I. — Blue-Greens, i, Phormidium. 2, Tetrapedia. 3, Aphanizomenon. 

 4, Anabaena. 5, Oscillatoria. 6, Merismopedia. 7, Rivularia. 8, 9, Micro- 

 cystis. 10, CcelosphKrium. 11, Nostoc. 12, Spirulina, 13, Apanocapsa. 



c. Filaments not attenuated and hair-like at the ends, 

 d. Filaments usually not branching ; where they show branching there 

 are no heterocysts. 

 e. Cells of the filament all of uniform size ; without heterocysts. 



Oscillatoriacetc. 

 f. Filament without sheath, 

 g. Filament multicellular, 

 h. Filament not a spiral (fig. 5) {^Oscillatoria), Oscillaria. 



hh. Filament a spiral. Arthrospira. 



gg. A single spiral cell (fig. 12). Spirulina. 



ff. Filament enclosed in a gelatinous sheath. 



