HOW TO KNOW THE FRESH-WATER ALGAE 



420a (418) Trichomes parallel within a fairly wide sheath; plant mass 

 developing bushy tufts; heterocysts basal in the trichome. Fig. 

 304 DESMONEMA 



Fig. 304. Desmonema Wrangelii 

 (Ag.) Born. & Flah. 



The falsely branched filaments 

 of this species differ from others 

 in the Scytonemataceae by hav- 

 ing several trichomes within 1 

 sheath. The filaments are gregarious and form plant masses of ma- 

 croscopic size on moist aerial substrates, and usually show erect tufts. 

 This is the only species reported from the United States. 



Figure 304 



420b Trichomes twisted and entangled in a wide sheath; heterocysts 

 intercalary. Fig. 305 DIPLOCOLON 



Fig. 305. Diplocolon Heppii Naeg. 

 (Redrawn from Smith). 



This plant forms an expanse on 

 moist aerial substrates such as drip- 

 ping rocky cliffs. The trichomes 

 are falsely branched, have inter- 

 calary heterocysts and are inclosed 

 several together in a wide gelatin- 

 P 3 nr ous sheath. 



Figure 205 »»«*%*»**. 



421a (376) Plants attached; cells club-shaped or with other shapes, 

 gregarious, forming cushion-like masses or horizontal expanses, 

 or solitary; epiphytic or growing on shells; cells usually showing 

 endospores (segments of the protoplast rounded up and forming 

 reproductive bodies which are spore-like) 422 



421b Plants not attached; cells mostly spherical, hemispherical, or rod- 

 shaped, not forming cushion-like masses nor horizontal expanses; 

 endospores lacking 427 



175 



