Chlorophyceae 45 



34 — Cells elongated, frequently curved; solitary or in definite loosely coherent colonies. .35 

 — Cells not elongated 37 



35— Colonies enveloped in mucus (fig. 3) '. Kirchneriella 



— Colonies with little or no mucus 36 



36 — Cells attenuated to acute spines. Cells forming definite colonies each of a single 

 row (fig. 14) Scenedesmus; cells solitary or loosely grouped in irregular bundles 



(figs 11, 12), Ankistrodesmus; cells lunate, arranged back to back (fig. 7) 



aelanastrum 



— Cells sublunate or ellipsoidal, arranged in groups forming irregular colonies 



Dimorphococcus 



37— Cells variable, united in a regular flat plate (fig. 26) ... • Crucigenia 



— Cells not united in a flat plate 38 



38 — Cells angular with a definite number of angles; cells solitary Tetraedron 



— Cells globose or subglobose 39 



39 — Cells strictly globose, united in a spherical colony. Sphere hollow (figs. 8, 9), Coelas- 



trum; sphere solid (fig. 16) Sorastrum 



— Cells not united in a spherical coenobium ' 40 



40— Cells with 2 or more attenuated bristles (fig. 13)— Phythelieae Richteriella 



—Cells without bristles 41 



41 — Cells generally retained within large wall of mother cell Oocystideae 



— Cells in grape like clusters, freely exposed in a thin gelatinous envelope (fig. 10), 

 Botrycoccus; cells with well marked subdichotomous connecting threads, chloro- 

 plast parietal (fig. 4), DIctyosphaerium ; cells in radiating series, connecting threads 

 scarcely visible; chloroplasts axial Dictyocystis 



42 — Cell division by intercalation of new cells producing transverse striation. Oedigoni- 

 ales. Cells long, without laterally placed bristles (fig. 30), Oedogonium; cells short 



with laterally placed bristle (fig. 6) Bulbochaete 



— Cell division of the ordinary type 43 



43 — Filament attenuated and commonly ending in a bristle — -Chaetophorales 44 



— Filaments not ending in a bristle 51 



44 — Plant of branched filaments forming a flat cushion like expansion enveloped in 



mucilage. Coleochaetaceae Coleochaeta 



— Plant entirely filamentous 45 



45 — Filaments branched 46 



— Filaments not branched 50 



46 — Gametes arise from special cells only Trentepohliaceae 



— Gametes arise from any cell of the filament 47 



47 — Small creeping filaments on water plants. Cells globose or cylindrical, Herpos- 



teiraceae. Herposteiron ; cells flask shaped, Chaetosphaeridiaceae .•.••• 



Chaetosphaeridium 



— Plants not creeping 48 



48 — Plants less than one mm. high, without setae Microthaminon 



— Plants larger, branches attenuated, and with setae 49 



49 — Filaments fine. Filaments showing little difference in character of stem and branch, 

 not in tufts in gelatinous masses, Myxonema ; filaments in tufts in a dense gelatinous 

 mass (fig. 27), Chaetophora; filaments and main branches large, bearing tufts of 

 small branches (fig. 32) Draparnaldia 



50 — Cells with thick lamellose coats, in a series inside a lamellose sheath. Cylindro- 



CAPSACEAE Cylindrocapsa 



— Cells without lamellose coat. Ulothrichaceae. Chromatophore a homogeneous 

 zonate band, with one to several pyrenoids (fig. 29), Ulothrix; chromatophore a 

 parietal disk or plate, with one pyrenoid, Stichococcus; chromatophore granular, 

 covering more or less completely the whole cell wall, containing starch but no 

 pyrenoids (fig. 28) Microspora 



