HOW TO KNOW THE FRESH-WATER ALGAE 



232b Cells oblong, not adjoined at the end walls. Fig. 165 



GEMINELLA 



Fig. 165. a, Geminella in- 



terrupta (Turp.) Lag.; b, 



5® ^(5) ® <S> C^(S» e^Q ^^ g. mutabilis (B r e b .) 



Wille. 



° These are filamentous 



pr^ r^\ rw^f^rw ^ f — V ^ P lants which have cylin- 



drical or broadly oval 

 cells encased in a wide 

 Figure 165 sheath of mucilage. The 



cells may be adjoined, or 

 rather evenly spaced one-half to 2 cell lengths apart. Like Hormidium 

 (Fig. 168) the chloroplast covers but a small portion of the wall. 



233a Cells quadrate or cylindrical; cell wall in 1 piece 234 



233b Cells globose, subglobose, or ellipsoid, wall usually of 2 over- 

 lapping pieces that meet in the midregion of the cell and form 

 short lateral projections (resulting from a rim about the cell in 

 center). Fig. 166 RADIOFILUM 



(mxmxrmmmyj) 



Figure 166 



Fig. 166. a, Radiofilum ilavescens G. S. West; b, R. conjunctivum 

 Schmidle. 



The globose or subglobose cells of these filaments help to separate 

 them from Geminella (Fig. 165) which also possesses a gelatinous sheath. 

 Some species (R. conjunctivum Schm., e. g.) have the wall in 2 sec- 

 tions which form a rather conspicuous overlapping in the mid region. 

 There are 3 species in this country, differentiated by shape and size 

 of the cells. 



106 



