rounded; sheath wanting; cells quadrate or a little longer than wide, 

 the dissepiments sometimes granular, sometimes scarcely discernible. 

 See note under Spirulina (p. 479). These plants may form thin 

 expansions, but more usually are found intermingled with other 

 algae, especially Oscillatoria spp. 



Key to the Species 



Trichomes 2.5-3.2m in diameter A. Gomontiana 



Trichomes 6-8/u in diameter A. Jenneri 



Arthrospira Gomontiana Setchell 1895, p. 430 



PI. 108, Fig. 21 



Trichomes very loosely spiralled, entangled to form free-floating 



flakes, bright blue-green, 2.5-3.2/x in diameter; cells 4-5/x long, with 



the dissepiments often scarcely discernible; cell contents vacuolate 



(?); width of spiral 4^6fx; distance between turns 16-1 8/x; forming 



floating patches of much entangled and actively twisting trichomes. 



Tychoplankter. Wis. 



Arthrospira Jenneri ( Kuetz. ) Stizenberger 1852, p. 32 

 PI. 108, Figs. 22, 23 

 Trichomes blue-green, scattered or gregarious, loosely coiled, not 

 tapering toward the apices, 6-8/* in diameter; cells quadrate, dis- 

 sepiments granular, 4-5/* long; spiral 10-15/* wide, distance between 

 turns 12-14/x. 



Intermingled with other Cyanophyta filaments on mud, or in 

 organic sediment which has collected on submerged plants. Com- 

 mon. Mich., Wis. 



OSCILLATORIA Vaucher 1803, p. 165 

 Filamentous and elongate, without a sheath (except in hormo- 

 gonous stages of filament development); straight, or twisted and 

 entangled; the mature plant showing a polarity with an apical 

 region, which is often attenuated, the basal end truncate; trichomes 

 solitary and scattered, or forming expanded plant masses and slimy 

 layers on submerged objects or on the bottom; microscopically 

 usually showing an oscillating or gHding movement, especially 

 active in the anterior portion of the trichome; apical cell smoothly 

 rounded, or swollen and capitate, sometimes with a distinct sheath- 

 like membrane, the calyptra; most species having cells much 

 shorter than their width, with or without constrictions at the cross 



[481] 



