Semi-Centennial Volume. 151 



Family I. OSCILLATORIACEiE. 

 Key to Genera. 



A. Sheaths not present. 



* Trichomes cylindrical, straight or nearly so, never forming 

 a regular spiral, free, apex of trichome straight or curved. 



1. Oscillatofia. 



* * Trichomes unicellular, forming a regular, more or less lax 



spiral 2. Spimdina. 



B. Sheaths present. 



* Filaments simple; sheaths cylindrical, firm; trichomes single 

 within the sheath ; apex of trichome straight. 



a. Filaments simple, more or less agglutinated by their 

 mucus sheaths 3. Phoy-midium. 



b. Filaments simple, free, free-floating or forming a matted 

 mass 4. Lyngbya. 



* * Filaments frequently branched; sheaths firm, lamellose, 



transparent or colored; trichomes several with the sheath. 



a. Sheaths solid, colorless, filaments prostrate, woven into 

 more or less compact membranaceous mass. 



5. Hypheothrix. 



b. Sheaths mucous, not lamellose, always transparent; tri- 

 chomes many within the sheath 6. Microcoleus. 



1. Oscillatoria. 



Kin/ to SjK'ries. 



I. Apex of trichome constantly straight, finally capitate. 



A. Trichomes tapering, 4-6 mic. in diam.; cells quadrate or shorter, 

 but never very short; plant mass light blue-green. . .0. agardhii. 



B. Trichomes not at all or briefly tapering, 6-8 mic; often inter- 

 rupted by inflated refringment cells O. anguina. 



II. Apex straight or curved, not tapering. 



A. Trichomes, 4-10 mic. in diam., slightly constricted at the joints; 

 cells, 2.6-5 mic. in length; transverse walls usually furnished 

 with two rows of granules O. tenuis. 



B. Trichomes, 2-3 mic. in diam., not constricted at the joints; cells, 

 4-8.5 mic. in length, commonly marked with two protoplasmic 

 granules O. amphibia. 



C. Trichomes, 1-1.5 mic. in diam., often rolled in circinate manner. 



O. subtilissima. 



D. Trichomes, 3.5-4 mic. in diam., not constricted at joints; trans- 

 verse walls not granulated O. chlorina. 



E. Trichomes, .6 mic. in diam., flexible, tangled, not constricted at 

 joints O. angnstissima. 



III. Apex of trichome tapering, more or less jointed, hooked or flexuous, 

 not entirely spiraled. 



A. Apical cell capitate. 



1. Trichomes, 2-3 mic. in diam., cells longer than their diam- 

 eter O. splendida. 



2. Trichomes, 2.5-5 mic. in diam., cells somewhat quadrate. 



O. amoena. 



B. Apical cell not capitate. 



1. Trichomes, 4-6.5 mic. in diam., here and there interrupted 

 by inflated refringent cells; apex of trichome briefly taper- 

 ing, hooked or flexuous; cells three times shorter than their 

 diameter O. brevis. 



