in diameter, 4-8/x long; not constricted at the cross walls, which 

 are granular; cell contents granular, especially at the cross walls. 

 Tychoplanktonic; on submerged vegetation. Wis. 



Phormidium lucidum ( C. A. Ag. ) Kuetzing 1843, p. 194 

 Filaments forming thick, firm mats which are dark green above 

 but colorless within. Trichomes somewhat parallel, either curved or 

 (at least at the ends) straight, and shghtly tapering, sometimes 

 ending in a point but with the apical cell capitate; calypti'a broadly 

 rounded; sheath diffluent and not colored by chlor-zinc-iodide 

 reagent. Cells very short, 7-8/x in diameter, 2-2.5/* long; slightly 

 constricted at the cross walls, which are granular. 

 Mich. 



Phormidimn minnesotense (Tilden) Drouet 1942, p. 136 

 Filaments forming a blue-green, thin expanse; individual sheaths 

 indistinct, confluent with the mucilage of the plant mass; trichomes 

 straight or slightly curved, parallel or somewhat entangled, not 

 tapering at the distal end; apical cell broadly rounded, not capitate, 

 and without a calyptra; cells short-cylindric, 2.5/x in diameter, 2-4/* 

 long, constricted at the cross walls. 

 Tychoplankter. Wis. 



Phormidium mucicola Naumann & Huber-Pestalozzi in 

 Huber-Pestalozzi & Naumann 1929, pp. 67, 68 

 PI. Ill, Figs. 4, 5 

 Filaments short, clustered or scattered in the mucilage of other 

 blue-green algae (Microcystis). Sheaths thin, inconspicuous, difflu- 

 ent. Trichomes parallel or scattered; up to 50/* long; not tapering 

 at the apices, which are broadly rounded or conical. Cells quadrate 

 to short-cylindric, 1.3-2/t in diameter, 1.8-3/* long; constricted at 

 the cross walls, often separated from one another; cell contents 

 pale blue-green. 



This species is a frequent inhabiter of colonies of Microcystis 

 aeruginosa, in which there may be far fewer Microcystis cells than 

 Phormidium filaments. 



Rather common in hard water; euplanktonic. Mich., Wis. 



Phormidium Retzii (C. A. Ag.) Gomont 1892a, p. 175 



PI. Ill, Fig. 6 

 Filaments forming thin, dark blue-green skeins or tufts on sub- 

 merged aquatics, or floating free; sheaths thin and inconspicuous, 

 diffluent; trichomes straight, parallel, not tapering at the apices, or 



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