14 Minnesota Algae 



D Plant mass gelatinous, brownish, growing on Z o s t e r a; sheaths 

 numerous, distinct; cells 9-1 1 mic. in diameter, 19-26 mic. in 

 length G. zostericola 



2 Sheaths sometimes lamellose 



(i) Plant mass blue-green or greenish; sheaths not distinctly lamellose 

 A Free-floating; cells .75-2.8 mic. in diameter G. punctata 



B On wet rocks; plants 4-8 mic. in diameter; cells 2-3 mic. in 

 diameter G. aeruginosa 



(2) Plant mass olive or green; plants 6.2-10 mic. in diameter; sheaths 



narrow, lamellose when old; cells 2.5 mic. in diameter 



G. gelatinosa 



(3) Plant mass dull olive; plants 7-1 1 mic. in diameter; sheaths thick, 



not at all or scarcely lamellose; cells 3-6 mic. in diameter 



G. conglomerata 



3 Sheaths not lamellose 



(i) Plant mass flesh-colored to yellowish; plants 2.5-5.5 mic. in diam- 

 eter; cell contents flesh-colored to honey-colored 



G. mellea 



(2) Plant mass black; plants 9-14 mic. in diameter; cells 3.5-4.5 mic. 

 in diameter; cell contents pale blue-green G. atrata 



II Sheaths yellowish or brownish 



1 Sheaths lamellose 



(i) Plant mass dull olive to brownish-green; sheaths colorless or yel- 

 lowish G. muralis 



(2) Plant mass grayish-brown to black; sheaths very thick, yellowish 

 or orange, becoming darker G. rupestris 



2 Sheaths sometimes lamellose 



(i) Plants 4.5-5.5 mic. in diameter; sheaths usually not lamellose; cells 

 1.5-2 mic. in diameter G. fusco-lutea 



(2) Plants 12 mic. in diameter; sheaths homogeneous or lamellose; 



cells 3-4.5 mic. in diameter G. sparsa 



(3) Colonies subglobose; sheaths somewhat lamellose; cells 9-15 mic. 



in diameter G. gigas 



3 Sheaths not lamellose; plant mass olive-green; plants 5-8 mic. in 

 diameter G. crepidinum 



III Sheaths violet, purple or red. 

 I Sheaths lamellose 



(i) Plant mass purple, sometimes becoming black 

 A Sheaths deep purple or copper-brown; plants 6-12 mic. in diameter 



G. magma 



B Sheaths violet or reddish-purple; plants 7.5-12 mic. in diameter; 

 cells 2-4.5 mic. J" diameter G. janthina 



