nn. Cells globose or subglobose. 



o. Cells strictly globose, united in a spherical colony, 

 p. Sphere (Ccenobium) hollow (figs. 8, 9) Ccvlastrum. 



pp. Sphere solid (fig. 16). Sorasfrum. 



00. Cells not united in a spherical ccenobium. 

 p. Cells with two or more attenuated bristles (fig. 13). 



PHYTHELIE^E. Richteriella. 

 pp. Cells without bristles, 

 q. Cells generally retained within enlarged wall of mother 

 cell. OocYSTiDE^i;. 



qq. Cells joined in colonies by persistent walls of mother 

 cells, which sometimes become transformed into 

 connecting threads, 

 r. Cells in grape-like clusters, freely exposed in a thin 

 gelatinous envelope (fig. 10) Botryococcus- 



rr. Cells indefinitely disposed. 

 s. With well-marked, subdichotomous connecting 

 threads, chloroplast parietal (fig. 4) 



Diciyosphceriutn . 

 ss. Cells in radiating series, connecting threads scarcely 

 visible ; chloroplast axile. Dictyocystis. 



ff . Thallus filamentous, though filaments may unite in a plane ; if uni- 

 cellular then conjugation takes place. 

 g. Cell division by intercalation of new cells producing transverse 

 striation. OEDOGONIALES. 



h. Cells long, without laterally placed bristles (fig. 30). 



Oedogoniuni. 

 .hh. Cells short, with laterally placed bristle (fig. 6) Biilbochcrte. 



%'g. Cell division of the ordinary type, 

 h. Filaments attenuated and commonly ending in a bristle. 



ch.etophorai.es. 



i. Plant of branched filaments forming a flat cushionlike expansion 

 enveloped in mucilage. Coleoch.^tace^. Coleoch(sta. 



ii. Plant entirely filamentous, simple, 

 j. Filaments branched, 

 k. Gametes arise from special cells only. TrenTEPohIvIACE.-E. 

 kk. Gametes arise from any cell of the filament. 



I. Small creeping filaments iipon water plants, 

 m. Cells globose or cylindrical. 



Herposteirace^. Herposteiron. 

 mm. As above but with flask shaped cell. 



CHAETosPHAERiDiACE.ii. Chaetosphaeridiiiiii . 



II. Plants not creeping. 



m. Plants less than one mm. high, without sette. 



Microthauiinoti . 

 mm. Plants larger, branches attenuated, and with setae. 

 n. Filaments fine. 



o. Filaments showing little diff'erence in character of stem 

 and branch, not in tufts in gelatinous masses. 



Myxoncina. 



