HOW TO KNOW THE FRESH-WATER ALGAE 



387b Trichomes lying in parallel bundles, not tapered at the anterior 

 end; apical cell never capitate. Fig. 278 TR1CHODESMIUM 



Fig. 278. 

 Kleb. 



Trichodesmium lacustre 



Figure 278 



This is a species of uncertain 

 position because it has an Anaba- 

 ena - like filament, but without 

 heterocysts. The filaments are ar- 

 ranged in parallel bundles which form free-floating, dark-green flakes. 

 The cells contain numerous pseudovacuoles (gas pockets). T. erythra- 

 ceum Ehr. is a marine species which, because of light refraction from 

 pseudovacuoles, produces a color that gives the Red Sea its name. 



388a (386) Sheath containing one trichome 



389 



388b Sheath containing more than one trichome 



394 



J89a Sheath firm and definite, not adhering to sheaths of adjacent fila- 

 ments 390 



389b Sheath soft and sticky, often adhering to sheaths of adjacent 

 plants and intermingling (confluent) with them 391 



390a Sheaths purple or reddish, conspicuously stratified. Fig. 279 .... 

 PORPHYROSIPHON 



Fig. 279. Porphyrosiphon Notarisii 



(Menegh.) Kuetz. 



The purple color of the lamellated 

 sheath of this species accounts for 

 the brightly colored patches on damp 

 soil in subtropical sections of the 

 country. There is but 1 species re- 

 corded for the United States. 



m 



f*T 



urn 



Figure 279 



390b Sheaths colorless or yellowish, not stratified, or indistinctly so. 

 See Fig. 272 LYNGBYA 



162 



