HOW TO KNOW THE FRESH-WATER ALGAE 



391a (389) Filaments forming an expanded plant mass with or without 

 erect tufts » • • 392 



391b Filaments not forming an expanded mass or stratum 393 



392a Plant mass having erect tufts. Fig. 280 SYMPLOCA 



Fig. 280. Symploca mus- 

 corum (Ag.) Gom. 



Filaments of this spe- 

 cies occur in erect tufts in 

 Figure 280 moist aerial situations. 



Species which have thin, 

 sticky sheaths should be compared with Phormidium (Fig. 281) with 

 which they may be confused if seen individually and not in colonial 

 mass. 



392b Plant mass without erect tufts. 

 Fig. 281 PHORMIDIUM 



Figure 281 



Fig. 281. a, Phormidium ambiguum Gom.; b, P. favosum (Bory) Gom.; 

 c, P. inundafum Kuetz. 



There are numerous species of this genus, differentiated by size 

 and by characteristics of the apical cell of the trichome. The 

 sheaths are thin and sticky, hence the plants form rather closely com- 

 pacted mats that coat over submerged surfaces. Such a mat when 

 handled does not break apart easily (as somewhat similar-appearing 

 growths of Oscillatoiia, Fig. 277, might do). The plant masses are 

 blue- or black-green in color and feel slimy or slippery to the touch. 



393a (391) Filaments lying parallel in free-floating bundles. See Fig. 

 278 TRICHODESMIUM 



163 



