BLUE-GREEN ALGAE 



113 



62 (61, 63) Sheaths thin; branches commonly unilateral. Hapalosiphon Nageli. 



Filaments free-floating amongst other algae or subaerial. 

 Branches long and flexuose, slightly attenuated, generally 

 narrower than the main axis and borne imilaterally. 

 Primary axis consisting of a single row, rarely of 2 to 3 

 rows of cells, enclosed in a strong sheath of uniform 

 thickness. Spores and heterocysts intercalary. Among 

 water weeds, in hot springs, etc. 



Fig. 63. Eapalosiphon hibernicus W. and G. S. West. 

 X 440. (After West.) 



63 (61, 62) Sheaths thick; fused to form an irregular gelatinous mass. 



Nostochopsis Wood. 



Forming rounded, Nostoc-like 

 masses, attached to water plants. 

 Filaments composed of but one cell- 

 row; profusely branched. 



Fig. 64. Nostochopsis lobata Wood. 

 X 33°. (After Bornet.) 



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64 (26) Filaments conspicuously attenuated towards one or both extrem- 



ities, which are generally piliferous. 



Suborder Trichophoreae 65 



Filaments sheathed, simple or branched, attenuated from the base 

 to the apex, which is piliferous; heterocysts generally basal, 

 rarely absent. . Family Rivulariaceae . 65 



65 (68) Filaments free or forming penicillate tufts or soft velvety expan- 



sions ... . . .66 



66 (67) Branches, when present, distinct and free. . . . Calothrix Agardh. 



Filaments simple or 

 slightly branched, single 

 in a thick sheath; hetero- 

 cysts basal or intercalary 

 or, in a few species, 

 absent. Forming tufts 

 or soft velvety expan- 

 sions on wet or sub- 

 merged rocks. 



Fig. 65. Calothrix thermalis 

 Hansgirg. X46s. (Origi- 

 nal.) 



67 (66) Branches several (2 to 6) within a common sheath. 



Dichothrix Zanardini. 



Filaments more or less di- 

 chotomously branched; hetero- 

 cysts basal or intercalary. On 

 wet rocks, etc. 



Fig. 66. Dichothrix inlerrupla W. 

 and G. S. West. X 420 (After 

 West.) 



68 (65) Filaments forming a hemispherical or globular mass, closely united 

 by mucus. . go 



