BLUE-GREEN ALGAE 105 



7 (4) Cells with thin cell walls Synechococcus Nageli. 



Cells comparatively large, cylindrical or ellipsoidal, living 

 usually singly or sometimes forming small families of two 

 to four united in a row or chain. Cell-contents blue-green, 

 sometimes yellowish, pinkish, or pale orange. Free-floating 

 in ponds and pools, or on rocks. 



Fig. 34- 



Synechococcus aeruginosus 

 Kirchner.) 



Nageli. X 575- (After 



8(3,11) Cell-division in two planes 9 



9 (10) Cells spherical or oblong, forming flat, plate-like colonies. 



Merismopedia Mey en . 



Cells usually adhering in groups of four, and arranged in reg- 

 ular rows to form a flat, rectangular, plate-like colony. In 

 plankton, in ponds, and lakes. 



Fig. 35. Merismopedia elegans ^..'QtdiXin. X 450. (After West.) 



10 (9) 



11(3,8) 



12 (23) 



13 (16) 



14 (15) 



Cells flat, quadrangular in outline, sohtary, or forming small 



colonies Tetrapcdia Reinsch. 



Cells with thin membrane; solitary or united into flat colonies of 2 to 16 

 cells. 



Cell-division in three planes 12 



Cells united into definite, often comparatively large colonies. 13 



Colonies more or less regularly spherical 14 



Colonies hollow; cells closely and regularly arranged at the surface. 



Coclosphaeriiim Xageli. 



Cells globose or oblong, forming on the surface of lakes and 

 ponds microscopically smaU, hollow, spherical colonies em- 

 bedded in a mass of mucus; reproduction by means of single 

 cells escaping from the colony as well as through the con- 

 striction of old colonies to form new ones. Common in fresh- 

 water plankton. 



Fig. 36. Coelosphaeriutn kutzingianum Nageli. X 465- (Original.) 



Colonies solid; cells sparsely scattered through the jelly, pyriform 

 in shape Gomphosphacria Kiitzing. 



Cells enclosed by a colorless gelatinous matrix to form micro- 

 scopically smaU, solid, globular, or ellipsoid colonies; the peripheral 

 cells grouped in pairs and egg-shaped or pyriform, or (during 

 division) heart-shaped. In ponds,^ stagnant water, etc. 



Fig. 37. Gomphosphaeria aponina Kiitzing. X 465- (Original.) 



16(13) Colonies, when old, generally not spherical i? 



17 (18, 19) Colonies microscopically small, solid, globular, or clustered. 

 ' ^ "^ Microcystis Kutzing. 



(Probably should be united with Clathrocystis .) Cells spherical, or through 

 pressure somewhat angular; uniting in great numbers to form microscopic- 

 ally small solid colonies. Common in ponds and ditches. 



15 (14) 



