Notes on the Blue-green Alga, etc. 
5. Filaments with false branches; sheaths firm and tubular 
Fam. II., Seytonemaceze 
5. Trichomes not branched ; cells in a single row, generally 
torulose, in a gelatinous mass .. Fam. III., Nostocacee 
Sub-Order II., TRICHOPHORE2. 
6. Trichomes tapering from base; apex piliferous ; 
heterocysts rarely absent .. Fam. V., Rivulariacez 
6. Trichomes tapering towards each end ; heterocysts 
absent fm 3 Soy be datehenls Wee Camptotrichaceze 
Order II., CoccoGoONE&. 
7. Unicellular, attached by the base to other alge; re- 
production by asexual non-motile spores 
Fam. I., Chamesiphoniacee 
7. Unicellular, usually in colonies in a gelatinous envelope, 
sometimes free Ae Ee .. Fam. II., Chroocoecaceze 
KEY TO GENERA OF OSCILLATORIACE#, 
I. Sheaths absent or ceed so 
I. Sheaths present 
2. Trichomes straight or curved 
2. Trichomes in a regular spiral 
3. Trichomes free; sheath absent or exceedingly thin, Oscillatoria 
3. Trichomes with delicate, hyaline sheaths, often difficult 
to see; filaments more or less agglutinated, mucus- 
like or diffluent .. .. Phormidium 
4. Trichomes in a regular spiral, multicellular, Arthrospira 
4. Trichomes in a regular spiral, unicellular .. Spirulina 
5. Several trichomes within a sheath ~: 
5. Not more than one trichome in a sheath .. is 
6, Sheaths firm, lamellose, coloured or ce ee 
6. Sheaths hyaline, more or less mucous. é 
7. Filaments branched or simple; trichomes may be densely 
aggregated in the sheath, which is usually coloured, Sehizothrix 
Te Sheaths with few trichomes, erro aue i or yellowish, 
not capitate 3. Dasygloea 
8. Trichomes few within a " sheath ; apex capitate 
(marine) be F .. Hydrocoleus 
8. Trichomes many in a sheath .. ay .. Mierocoleus 
9. Filaments simple : ye i ; 
g. Filaments often with false branches : 
1o. Filaments free; trichomes surrounded by a firm: 
sheath .. ¥: Lyngbya 
10. Trichomes with delicate hyaline sheaths .. Phormidium 
ir. Plant mass dense, with tufts of filaments; sheaths 
colourless, thin, firm; false branches solitary Symploca 
11. Filaments free or forming felt-like masses, sometimes 
floating; filaments branched like Scytonema, but 
no heterocysts are present; sheaths usually colour- 
less, rarely yellowish, firm (genus frequently included 
in Scytonemacez) .. fe nie Ee ..  Plectonema 
KEY TO SPECIES OF OSCILLATORIA AND PHORMIDIUM. 
. Trichomes attenuate or tapering at the apex 
helen not attenuate nor ere at the apex 
. Acute attenuate .. : 
2. Obtuse or capitate 
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