HOW TO KNOW THE FRESH-WATER ALGAE 



241a (189) Plants composed of cells or of cellular units; cross walls 

 present 242 



241b Plants multinucleate filaments (coenocytes), without cross walls 

 (except when reproductive structures are developed and separated 

 by a cross partition from the main filament) 281 



242a Plants growing on moist soil with rhizoidal branches composed 

 of long, narrow cells; apical cell usually with a cap (thimble). 

 Fig. 174 OEDOCLADIUM 



Fig. 174. Oedocladium Hazenii Lewis, portion 

 of branched filament with an oogonium and 

 2 epiphytic male plants. 



This genus includes but 3 or 4 species in 

 this country, growing on damp soil. There 

 may be many species in the genus but are 

 unknown because collections are so seldom 

 made from soil, and because in superficial ma- 

 croscopic appearance the growth may be mis- 

 taken for moss protonema. 



Figure 174 



242b Plants aquatic; parasitic on higher plants, or if terrestrial, without 

 long narrow rhizoidal branches and without terminal cap .... 243 



243a Plants prostrate, growing horizontally; mostly epiphytic or endo- 

 phytic; upright branches sometimes lacking; forming discs or flat 

 expansions 244 



243b Plants not growing entirely prostrate, at least in part with erect 

 branches; free-floating, parasitic on higher plants, or perforating 

 wood and shells 256 



244a Thallus a freely-branched filament; cells usually bearing setae 

 or hairs 245 



244b Thallus not freely-branched but forming a disc or flat expansion 

 of cells; sometimes forming a false cushion (pseudoparenchyma- 

 tous) 251 



111 



