g. Only a single filament with one sheath, 

 h. Sheath thick, slimy, filaments often bent, agglutinated (fig. l). 



Phoniiidiutn. 

 hh. Sheath firm, not slimy, 

 i. Filaments not consolidated into bundles. 



Lyngbya. Hypheothrix. 



ii. Filaments in crest or prostrate bundles. Syviploca. 



gg. Usually several filaments in a more or less thick sheath. vSeveral 



genera. 



ee. Filaments with occasional cells of different color or of larger size 



(heterocysts). Nostocace.<E. 



f. Filaments contorted, within a definite gelatinous tegument (fig. ii). 



No'itoc. 

 flf. Filament more or less straight, free or in a formless slimy mass, 

 without tegument, 

 g. Heterocysts not terminal. 



h. Filaments aggregated without order (fig. 4). Anabtena. 



hh. Filaments in bundles of plate like masses (fig. 3). 



Aphanizoinenon. 

 gg. Heterocysts terminal ; spores long and cylindrical, 



Cylindrospcrniim. 

 dd. I'ilaments branching, 

 e. F'ilaments showing true Ijranching. vStigonemace.^^. 



ee. Filaments showing false branching ; heterocysts present. 



SCYTONEMACE.^. 



cc. Filaments (trichomes) conspicuously attenuated towards one or both 

 extremities, which are generally hairy. Rivut,ARr.\CE-^. 



Filaments each with a basal heteroc3'st ; filaments radiating, in a 

 gelatinous mass (fig. 7). A'ivitlaria, G/ivofrichia. Several other 

 genera belong to this family. 

 aa. Cells green, red, or brown, 

 b. Organism green, not yellowish green ; if reddish then unicellular. 

 c. Organism with whorls of leaves. 



CHARACEiE. C/iara and Nitella. 

 cc. Organism smaller, without whorls (see illustration II). 



CHLOROPHYCEJE. 

 d. Thallus tubular, multinuclear, cell division not a]>parent ; usualh- 

 branched. SIPHONALES. Vaiicheria. 



dd. Thallus filamentous and septate, or unicellular, or expanded, 

 e. Thallus expanded, membranous. ULVALES. 



ee. Thallus neither expanded nor membranous, 

 f. Thallus not filamentous ; no conjugation. PROTOCOCCALES. 



g. Unicellular, or of a definite number of ciliated motile cells. 



VOLVOCACE.<^. (See illustration VI). 

 h. Composed of colonies of many cells ; cells with 2 cilia, 

 i. Colonies spherical or circular, 

 j. No gelatinous cover, 

 k. Many cells in a hollow globe (fig. 3). Volvox. 



kk. Cells 16, arranged in four rows. Spondyloinoruin. 



