178. Thallus not embedded in soft mucilage but tough and carti- 

 laginous, somewhat rigid, and maintaining its shape when re- 

 moved from the water -179 



179. Thallus much branched, the branches antler-like and irregularly 

 dichotomous; axes gradually tapering throughout Tuometja 



179. Thallus not at all or but very little branched, stiff and spine- 

 like with definite nodal swellings and intervening contractions — . Lemanea 



180. Plants yellow, yellow-brown, or dark golden-brown (see 



Diatoms: Appendix) 226 



180. Cells with chromatophores or protoplasts of other colors than above 181 



181. Chromatophores pale yellow-green (often appearing grass- 

 green; iodine test required; see illustrations of representative 

 forms), with xanthophyll predominating, often showing a metal- 

 lic lustre; reserve food oil or glycogen, the iodine test for starch 

 negative; cell wall often composed of 2 pieces; mostly non- 

 motile - 189 



181. Cells with protoplasts or chromatophores not yellow-green 182 



182. Cells with bright blue-green protoplasts or chromatophores 183 



182. Cells with protoplasts or chromatophores some other color 185 



183. Plants consisting of 1 or 4 spherical cells with a cup-shaped, 

 blue-green protoplast, inclosed by a mucilaginous sheath, each 



cell bearing a long, gelatinous bristle Gloeochaete 



183. Plants some other form; not bearing setae 184 



184. Plant a linear series of globose or oblong cells within a gelati- 

 nous strand; chromatophores stellate Asterocytis 



184. Plant an aquatic unicell, or composed of cells clustered in small, 

 spherical famiHes within the old mother cell wall; protoplasts 

 blue-green, chromatophore-like bodies (blue-green algal cells 

 endophytic in colorless host cells) Glaucocystis (in part) 



185. Cells appearing gray or brownish, in compact colonies and in- 

 closed by an orange-colored or brown, rubbery mucilage which 

 obscvtres the pigmentation of the cells Botryococcus (in part) 



185. Cells reddish, red, or violet-red - - 186 



186. Plant a gelatinous colony of ovate or globose cells with lamellate 

 sheaths, the green chloroplast masked by an abundance of 

 haematochrome Gloeocystis (in part) 



186. Plant not a gelatinous colony; cells soHtary or gregarious but not 

 invested by a colonial envelope 187 



187. Plants terrestrial; solitary or gregarious; spherical unicells form- 

 ing blood-red patches or layers on damp soil, especially in 

 greenhouses Porphyridium 



187. Plants aquatic 188 



188. Cells fusiform, with 1 long (rarely short) flagellum; green chloro- 

 plasts masked by haematochrome; sometimes forming red films 



on the surface of ponds -- .Euglena (in part) 



188. Cells round or ellipsoid; flagella 2, or wanting when cell is en- 

 cysted and quiescent; usually forming a rusty-red layer on the 

 bottom in shallow rain-water pools, etc Sphaerella (in part) 



189. Plants filamentous ._ — - 190 



189. Plants not filamentous; cells solitary or colonial 192 



190. Filaments false, consisting of branched gelatinous tubes with 1 or 



2 spherical cells at the distal ends of the segments... Mtsc/iococcus (in part) 

 190. Filaments not false; unbranched 191 



[586] 



