244 Minnesota Algae 



Genus STIGONEMA Agardh. Syst. Algar. 20. 1824. 



Plants terrestrial or aquatic; plant mass rigid, blackish brown, or 

 cushion-like and soft; filaments free, rarely laterally aggregated, scattered; 

 (richomes, in the larger filaments, consisting of two or several rows of 

 cells; heterocysts often lateral, here and there intercalary, hormogones 

 developed in the apices of vegetative branches or in short special branches. 



I Trichomes in the mature filaments consisting usually of a single row 



of cells 



1 Filaments 7-15 mic. in diameter; sheaths usually colorless 



S. hormoides 



2 Filaments 25 mic. in diameter; cells 14 mic. in diameter, 6-8 mic. in 



length S. aerugineum 



3 Filaments 24-26 mic. in diameter; sheaths thick, lamellose 



S. panniforme 



4 Filaments 14-38 mic. in diameter; sheaths yellowish brown 



S. tomentosum 



5 Filaments 24-45 mic. in diameter; sheaths thick, lamellose, colorless 



or yellowish brown S. ocellatum 



II Trichomes in the mature filaments consisting usually of two or several 



rows of cells 



1 Filaments up to 35 mic. in diameter 



(i) Filaments 18-28 mic. in diameter; cells often surrounded by a 

 special darker colored envelope S. minutum 



(2) Filaments 27-37 ™ic- in diameter; cells throughout the entire 

 length of the filament uniformly divided S, turfaceum 



2 Filaments 40-90 mic. in diameter 



(i) Hormogones 45 mic. in length, terminal, solitary or in series 



S. informe 



(2) Plants rigid; hormogones 45 mic. in length, lateral 



S. mamillosum 



Species not well understood 



S. brandegeei 



448. Stigonema hormoides (Kuetzing) Bornet and Flahault. Revis. des 

 Nostoc. Ann. Sci. Nat. Bot. VII. 5: 68. 1887. De Toni. Syll. Al- 

 gar. S: S77- 1907. 



West and West. On some Freshwater Algae -from the West Indies. 

 Journ. Linn. Soc. Bot. 30: 272. 1895. Collins. Algae. Flora of the Blue 

 Hills, Middlesex Fells, Stony Brook and Beaver Brook Reservations of 

 the Metropolitan Park Commission, Massachusetts. 128. 1896. Collins, 

 Holden and Setchell. Phyc. Bor.-Am. Fasc. 6. no. 259. 1897. West and 

 West. A Further Contribution to the Freshwater Algae of the West Indies. 

 1. c. 34: 286. 1899. Setchell. Notes on Cyanophyceae. — III. Erythea. 7: 

 47. 1899. Collins. Algae of the Flume. Rhodora. 6: 230. 1904. 



Plant mass thin, somewhat woolly, brownish black; filaments 7-IS 



