21. Plant a definite colony or an aggregate of individuals either ad- 

 joined or lying free from one another, sometimes invested by mucilage— .22 



21. Plant a branched or unbranched filament, either a series of cells, 

 or a tubular coenocyte (without cross walls), or filaments form- 

 ing an attached, cushion-like thallus - - 116 



22. Colony of cells invested by a common mucilaginous sheath, or 

 gelatinous matrix, (often close and discerned with difficulty; 



see Dictyosphaerium) 23 



22. Colony or aggregate of cells not invested by a common muci- 

 laginous sheath— 47 



23. Colony attached or adherent to a substrate 24 



23. Colony free-floating (sometimes entangled among other algae, 



but not attached to them).. - 31 



24. Colony saccate, bullate, intestiniform (PI. 5, Figs. 1,3), or 

 cushion-like when growing on moist substrates ( PI. 3, Figs. 8,9); 

 usually macroscopic — - 25 



24. Colony shaped differently; microscopic 26 



25. Cells in 2's and 4's, bearing long, fine pseudocilia ( PI. 5, Figs. 

 6, 11) which extend far beyond the Umits of the colonial muci- 

 lage; plants aquatic— — -— Tetraspora (in part) 



25. Cells without pseudocilia; plants mostly aerial, living on moist 

 substrates -- Palmella (in part) 



26. Colony pyriform, narrowed to form a stipe-hke basal attaching 

 portion; cells arranged at the periphery of the colonial mucilage 



(often showing long pseudociha) — - ...-. Apiocystis 



26. Colony shaped differently; without pseudocilia - — — - — 27 



27. Colony fusiform; cells fusiform (PI. 4, Figs. 1,2), solitary or in 

 linear pairs within the colonial mucilage and arranged with their 

 long axes parallel; colony usually free-floating but may be at- 

 tached when young—. -- Elakatothrix (in part) 



27. Cells not fusiform and not contained in a fusiform sheath — 28 



28. Cells elliptical or subspherical, arranged in 2's and 4's within 

 ungelatinized walls of mother cell; many cells inclosed by a 

 common mucilaginous investment; a red pigment spot and an 



apical papilla often visible Palmella stage of Chlamydomonas 



28. Cells spherical or ovoid, scattered irregularly throughout the 

 colonial mucilage, not inclosed within walls of old mother cells; 

 pigment spot lacking — 29 



29. Colony composed of cells inclosed in shapeless masses of muci- 

 lage, with individual cell sheaths confluent with the common gelatine -30 



29. Colony irregular, but keeping a definite shape; cell sheaths not 

 confluent with the colonial mucilage, but definite and often 

 lamellate (PI. 3, Fig. 17); plants aquatic or growing on moist 

 soil, but becoming red in some species when exposed to strong 

 illumination - Gloeocystis (in part) 



30. Cells all the same size within the colofiial mucilage; individual 

 cell sheaths sometimes scarcely discernible; chloroplast a parietal 



cup incompletely covering the cell wall — ....Palmella (in part) 



30. Cells of various sizes within the colonial mucilage; cell sheaths 

 not present; chloroplast a parietal cup which covers the entire 



wall — - -- - ..Chlorococcum (in part) 



31. Colonies forming stringy, intestiniform or expanded and often 

 clathrate, floating, gelatinous masses; pale green in color; macro- 

 scopic Free-floating, older thalli of Tetraspora 



[573] 



