HOW TO KNOW THE FRESH-WATER ALGAE 



393b Filaments irregularly intermingled, not arranged in free-floating 

 bundles. Fig. 28P/2 PHORMID1UM 



Figure 281Vi 



Fig. 281 ¥t. Phormidium sp. Isolated filament. 



394a (388) Sheaths soft and sticky, without an even, definite outer boun 

 dary 



395 



394b Sheaths firm and definite, not mucilaginous 396 



395a Sheaths containing 2 or 3 trichomes. Fig. 282. . . HYDROCOLEUM 



Fig. 282. Hydrocoieum oligoiri- 



chum A. Braun. 



In this genus there are only 3 

 (sometimes 4) trichomes within a 

 wide, lamellate, gelatinous sheath. 

 Figure 282 The filaments may be solitary or 



spread in a thin layer on damp soil. H. oJigofrichum usually is lime- 

 encrusted, whereas H. homeotrichum Kuetz. is not. 



395b Sheaths containing many trichomes. Fig. 283 M1CROCOLEUS 



Fig. 283. a, Microcoieus vagi- 

 natus (Vauch.) Gom.; b, M. 

 lacustris (Rab.) Farlow. 





There are several species of 

 this genus, differentiated by 

 size and character of the apical 

 cell. Unlike Hydrocoieum (Fig. 

 282) there are many intertwined 

 trichomes in each sheath. Usu- 

 ally the trichomes show an ac- 

 tive slithering motion over one another, may emerge from the end of 

 the sheath and then retract. The thallus is often of macroscopic size 

 as it grows on damp soil. Some species are more often found on 

 submerged substrates, however. 



Figure 283 



164 



