BLUE-GREEN ALGAE 



62 (6 1, 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 unilaterally. 

 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. Hapalosiphon hibernicus W. and G. S. West. 

 X440. (After West.) 



63 (6 1, 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 330. (After Bornet.) 



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 inter rupta W. 

 and G. S. West. X 420. (After 

 West.) 



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

 by mucus 69 



