HOW TO KNOW THE FRESH-WATER ALGAE 



256b Plants not parasitizing tissues of Angiosperms 257 



257a Cells without setae; filaments not tapering to hair-like tips . . . 258 

 257b Cells bearing setae or with branches tapering to fine points . . 276 



258a Branches short, irregular and rhizoidal, often formed only near 

 one end of the filament 259 



258b Branches long, multicellular, usually forming a definite pattern 

 of growth, opposite or alternate on the main axis 261 



259a Chloroplast a spiral ribbon. See Fig. 147 SPIROGYRA 



259b Chloroplast not a spiral ribbon 260 



260a Chloroplast an axial plate or band. See Fig. 145. . .MOUGEOTIA 



260b Chloroplast a parietal network of thickenings and thin strands. 

 See Fig. 158 RH1ZOCLONIUM 



261a Growing in wood, shells, or within limestone. Fig. 184 



GOMONTIA 



Fig. 184. Gomontia Holdenii Collins, 

 habit of thallus showing erect branch- 

 es. 



These plants must be sought within 

 old wood, shells, or in limestone de- 

 posits. The thallus occurs as a cushion- 

 like, irregularly tangled mass of short 

 filaments from which some elements 

 Figure 184 grow downward to form rhizoidal pene- 



trating threads. Reproductive structures 

 (sporangia) are borne on the upper part of the thallus or on the ends 

 of short erect branches. Most species are marine. 



261b Not growing in wood nor in shells 262 



262a Growing on trees or moist rocks; many or all cells showing an 

 abundance of orange or reddish-yellow pigment (haematochrome). 

 See Fig. 171 TRENTEPOHLIA 



262b Plants growing elsewhere, not containing haematochrome 263 



263a Thallus encrusted with lime 264 



263b Thallus not encrusted with lime 265 



116 



