]_g THE FLORA OF NEBRASKA. 



Xostoc 111 nscorniii Ag. Dispos. Alg. Suec. 44. 1810. 



Terrestrial; masses at first globose, then confluent and forming gelatinous 

 cushions adhering to the substratum; spores oval; sheaths confluent; 



cells 3 // in diam. , „ ,, , „ 



On wet rocks and on the moss covering them; hardly more than a form of 



N. commune. 

 Nostoc prnniforme (Roth) Ag. 1. c. 45. 

 IAnkia pruniforme Roth Catal. 111. 1806. 



Masses sub-globose or elliptical; from % mm. to 1 cm. or more; olive or dark 

 green becoming blackish brown; sheath coriaceous; filaments loosely in- 

 terwoven; cells globose, compressed by crowding; heterocysts globose; 

 cells 3-5 i-i in diam. 

 In still water. PI. L, Fig 4, a and 6. 



2. ANABAEM Bory Oscil. 1823. 



Filaments moniliform, without sheath or rarely sheathed, composed of sub- 

 globose cells some of which become changed into globose or elongated, 

 usually yellowish or brown spores; heterocyst intercalated in the fila- 

 ment; spores not arising in the cells contiguous to the heterocyst. 

 Etymology: Greek avaflaivo, go up. 

 Anabaena nos-aqnae (Lyngb.) Kuetz. Phyc. Gener. 209. 1843. 

 Nostoc flos-aquae Lyngb. Hydroph. t 68. 1819. 



Free-swimming, membranaceous, blue-green; filaments more or less curved, 

 often circinate; cells spherical or from mutual pressure elliptical or quad- 

 rate; heterocysts intercalated, elliptical; spores globose. 

 Var— circinalis (Rabh.) Kirch. 



Anabaena circinalis Rabh. Fl. Eur. Alg. II., 183. 1865. 



Filaments very much coiled and cells larger; spares and heterocyst not much 



larger than the vegetative cells. Cells 7-10 /j. in diam. 

 Gives a bluish-green color to stagnant water, or in age forms a blue-green 

 scum on the surface. PI. I., Fig. 12. 



3. SPHAEROZYGA Ag. in Regensb. Flora. 1827. 



Filaments sheathless, single or united in an indefinite gelatinous 

 stratum, or rarely in a definite sheath; heterocysts intercalcated, binary 

 or solitary; spores proximate to the heterocyst. 



Etymology: Greek ofyaipa, ball, and $vyov, yoke. 

 Spliaerozyga polysperma (Kuetz ) Rabh. Fl. Eur. Alg. II., 192. 1865. 

 Cylindrospermum polyspermum Kuetz. Phyc. Gener. 212. 1843. 



Filaments solitary or interwoven, blue-green, straight or variously curved, 

 articulations globose or short cylindrical; heterocysts globose or very 

 broadly elliptical, equal to or twice the diameter of the vegetative cells; 

 spores more or less elongated, densely granular, with rather thick mem- 

 brane; cells 3-6 ji in diam.; heterocyst 7-9 /i in diam. 



In stagnant water usually among other algae; also on damp earth, on flower 

 pots, etc., in greenhouses at the University. PI. I., Fig. 8. 

 Sphaerozyga smith ii (Thwaites) Wolle Fw. Alg. 290. 1887. 



Dolichospermum smithii Thwaites Ann. Mag. Nat. Hist., II., 5, PI. IX., Fig. 4. 



Filaments single, or two or three in a sheath, straight; sheath sometimes dif- 

 fluent, 32 n; articulations globose, equal to or somewhat longer than the 

 diameter, 4-6 //; heterocyst oval, or globose 8-9x9-23 /*; spores cylindrical' 

 2-3 times as long as wide, 10-12x20-32 /i. 



In moist places in greenhouses. PI. I., Figs. 9 and 10. 



