THE FLORA OF NEBRASKA. 17 



Cell mass more or loss definite, lighl aeruginous or gray green; cells glo- 

 bose, or more or less oval or oblong al division, 3 5/iin diam.; cell mass 



composed of 1 64 ceils, rarely more. 

 Ponds ami sluggish water, not uncommon. PL I . I 



Merismopedia convolnta Bbeb. in Kuetz. Sp. Alg. 172. 1849. 



Cell-masses membranaceous, visible to the naked >ye, folded or co 



families composed of groups of geminate cells; cells spherical or oblong, 

 4 [i; cell-contents homogeneous, bluish green. 

 At the bottom of pools, or floating upon the surface. 



Mv\ 'ismopedia violacea Kuetz. 1. c. 



Cell-masses very minute, tubular, cells I 32, about 1 ,» in diam., violet. 

 Quite common in stagnant ponds about Thedford, forming violet or purplish 

 slimy masses sometimes reaching the size of one's hand. Easily distin 



guisbed from the foregoing species by its smaller size and violet color. 



Order II.— NEMATOGrENEA-E. — Multicellular or pseudo-multicellular, forming 



a simple or branched filament, usually enclose. I La a tubular, homoge 

 neous, or lamellate sheath. 



Family.-NOSTOCACEAE. 



Mass gelatinous or membranaceous, enclosed in a more or less firm sheath, definite, 

 globose, or variously expanded; filaments flexuously curved irregularly interlaced, cells 

 globose or elliptical, distinct or more or less closely connected ; heterocysts terminal or 

 intercalated, larger than or equal to the other cells; spores equal to the heterooysl 

 or a little larger, green, becoming greenish blue, olivaceous, or yellowish brown. 



SYNOPSIS. 



Nostoc. -Filaments concatenate, sheathed ; heterocyst intercala: 



Anabaena. — Filaments moniliform, without a sheath; heterocyst usually intercalated. 



Sphaerozyga.— Filaments sbeatbless; heterocyst intercalated, binary or solitary; spores 



proximate to heterocyst. 

 Cylindrospermum. Filaments sheathless, heterocyst terminal, cylindrical; spon 

 tiguous to heterocyst. 



1. XOSTOC Vadch. Hist. Conf. 1803. 



Mass gelatinous, of various shapes; heterocysts usually intercalate 



about the size of the heterocyst or a little larger. 

 Etymology unknown. 



The nostocs are said to be merely arr sted stages in the 1 relopmenl of Borne 

 of the higher protophytes, as Scytora na. 1 1 • • ver this may be, as frequently 

 happens in such cases, they reproduce themselves from generation i 

 ation without ever attaining any higher developm< nt. 



Nostoc commune Vauch Let. 16 f. 1. 



Terrestrial; mass at Qrsl globose, becoming tongue-shaped, plane, or irregular; 

 mature mas- suborbicular, folded, undulate, >ntir< »r lol ed, often perfor 

 ated or expanded; cells 5-6 in diam. 

 Frequent on damp earth and in stagnant >r running water. In some parte 

 of the state it is found covering the ground tor some distance in damp 

 places. 



