32 GENERA OF ALG^F. 



R. Parasitic; sheaths thin; cells short, tubular . Chamtzsiphon, 100 



R. Not parasitic (S). 



S. Agglutinated in erect, wick-like clusters, articulate, base prostrate, 



Symploca, 102 



S. Not agglutinated; exceptionally appearing branched; often form- 

 ing a stratum Lyngbya, 101 



T. Filaments parallel in dense clusters; free-swimming, 



Aphanizomenon, 96 



T. Filaments short, heterocysts at their base; not free-swimming, 



Masligonfma, 82 



T. Filaments slowly motile Oscillaria, 104 



T. Filaments not motile (U). 



U. Filaments very slender, articulations more or less indistinct, 



Leptothrix, 106 



U. Filaments cruciformly branched Aster othrix, io6a 



V. Free-swimming, (/. e. not adherent), (W). 



V. Not free-smimming (X). 



W. Cells globose, or oblong when dividing, in a single, quadrate 

 layer, bluish-green Merismopedia, 112 



W. Cells globose, sometimes in a small colony, brownish or red,, 

 sometimes greenish Chlamydococcus, 38 



W. Cells wedge-shaped, in radiating families . Gomphosphceria 115 



W. Cells filamentous or ring-like, spirally twisted, usually motile, 



Spirillum, 107 



W. Cells filiform, very minute, spirally twisted . , Spirulina, 108 



X. Sheath present, gelatinous or jelly-like, often colorless (Y). 



X. Sheath none; cells spherical or angular by pressure, solitary or in 

 small families Chroococcus, 121 



Y. Aquatic (a). 



Y. On moist timbers and earth; cells small, in globose bodies in a 

 thin membrane Microcystis, 1 1 6 



a. Sheaths thin, not confluent; cells tubular, short, parasitic, 



Cham&siphon, 100 



a. Sheaths confluent, in a mucous stratum, or elongation or membra- 

 nous (b\ ^ 



a. Sheaths bladder-like, colorless; cells cylindric, ends rounded, 



Glceothece, 109 



b. Sheaths confluent (c). 



b. Sheaths membranous (/). 



c. Cells spherical or nearly so (d). 

 c. Cells not spherical (e). 



