HOW TO KNOW THE FRESH-WATER ALGAE 



396a (394) Sheaths wide, containing 2 or 3 loosely arranged trichomes. 

 Fig. 284 DASYGLOEA 



Fig. 284. Dasygloea sp. 



The sheaths of the plants in this 

 genus are rather firm and definite 

 in outline, contain but 1 to 3 tri- 

 chomes. See D. amorpha Berk. The 

 sheaths are usually forked or 

 branched at the ends (as they are 

 also in Schizothrix, Fig. 285, with 

 Only one species is reported from 



Figure 284 



which it should be compared) 

 the United States. 



396b Sheaths close, usually containing several crowded trichomes. Fig. 

 285 SCHIZOTHRIX 



Figure 285 



Fig. 285. Schizothrix tinctoiia Gom. 



In this genus theie are but few trichomes within a definite and 

 rather firm sheath. The plant masses are of macroscopic size and 

 often form streaming masses, or films and wefts over submerged 

 vegetation. Several of the species quickly disintegrate when stored in 

 a covered container for a short time without preservative and liberate 

 a copious amount of the phycocyanin pigment which is present in 

 blue-green algae. There are at least a dozen species reported from 

 the United States, differentiated by size and cell proportions. 



397a (381) Trichomes tapering from base to apex 398 



397b Trichomes not tapering from base to apex 402 



398a Filaments inclosed within abundant mucilage, forming a globular 

 or hemispherical body, attached or free-floating 399 



398b Filaments not inclosed by abundant mucilage to form a thallus 

 of definite shape , 401 



165 



