254. Plant a spirally twisted, long or short unicell, usually showing 



oscillating or spiral movements.— Spirulina (in part) 



254. Plant otherwise 255 



255. Plant an epiphyte, a sheathed, club-shaped unicell usually show- 

 ing endospores (PI. 108, Figs. 5, 6), which are cut off success- 

 ively from the apex of the protoplast Chamaesiphon 



255. Plant soUtary or colonial, not forming endospores; not a club- 

 shaped unicell - 256 



256. Cells embedded in a mucilaginous sheath which may be lamellate 262 



256. Cells not embedded in a common mucilaginous or gelatinous matrix... .257 



257. Cells globose 258 



257. Cells longer than vdde, oblong or cylindrical 259 



258. Cells minute, 1-5ac in diameter, sohtary or gregarious (usually 



with a sheath, but this is often not apparent). Chroococcus (in part) 



258. Cells larger, up to 50m in diameter (colorless host cells with 

 vermiform, endophytic blue-green protoplasts) Glaucocystis (in part) 



259. Cells sohtary or sometimes in famihes of 2-4; oblong or broadly 



ovate to subcyhndrical, up to 50m in diameter 261 



259. Cells in small colonies or rarely solitary, cylindrical, strongly 

 curved or pyriform — — 260 



260. Cells in small clusters, sometimes sohtary, strongly curved, de- 

 scribing nearly a complete circle, sometimes lying with long axes 

 parallel in compact series within the mucilage of other algae ..Cyanarcus 



260. Cells pyriform, radiately arranged in small colonies and inclosed 

 by an inconspicuous gelatinous investment, which is invisible 



unless stained.— -... - Marssoniella 



261. Cells ovate, sohtary or in famihes of 2 to 4, inclosed by old 

 mother cell wall (colorless host cell with endophytic blue-green 

 protoplasts), up to 50m in diameter Glaucocystis (in part) 



261. Cells oblong or subcyhndrical, up to 15m in diameter, not sym- 

 biotic as above Synechococcus 



262. Cells globose, 2-16 in a mucilaginous sheath in which individual 

 cell sheaths are visible; free-floating or adherent, sometimes 

 subaerial Chroococcus (in part) 



262. Cells globose, cylindrical, or elongate, forming many-celled 

 colonial aggregates of more than 16 individuals, inclosed by 

 copious mucilage which may or may not be lamellated 263 



263. Cells 10 or more times their diameter in length, cyhndrical, 

 reniform, or fusiform 264 



263. Cells 2 or 3 (rarely as much as 8) times their diameter in 

 length; round, ovate, or short cylindric 265 



264. Cells narrowly fusiform, wdth tapering, blunt-pointed 



apices Dactylococcopsis 



264. Cells reniform or vermiform, straight or variously curved —Rhabdoderma 



265. Cells minute, 0.6-1.5m in diameter, bacilhform, crowded within a 

 colorless colonial mucilage; pigment scarcely discernible Pelogloea 



265. Cells larger, or not bacilliform; pigment readily discernible ...- 266 



266. Cells oblong or short cyhndric, with poles rounded, crowded 

 and irregularly arranged in copious mucilage; individual cell 

 sheaths sometimes evident {Anacystis, in part) 



Including: a. Aphanothece, vdth individual cell sheaths not apparent; 

 b. Gloeothece, v^dth individual cell sheaths apparent. 



[ 591 ] 



