32 FRESH-WATER ALG^ OF THE UNITED STATES. 



the only differences between them and the European plant are that they are not so 

 large, and do not agree in color, many of them being browner; but these are certainly 

 insufficient grounds for separating them. Prof. Rabenhorst speaks of observing 

 the contents of heterocysts dividing up so as to form a little colony of cells, which 

 finally break through the maternal wall. 1 have only studied mounted specimens, 

 but have seen very clearly heterocysts in which this process was taking place, 



T¥. punctatnm, Wood, (sp. no v.) 



N. terrestre ; thallo expanso orbiculare vel nonnihil irregulare, tenuissimo, asrugineo, parvo 

 membranaceo, pellucidulo; trichomatibus laxe intricatis, varie curvatis, articulis globosis vel 

 ssepius ellipticis, plerumque medio pellucidulis, laxe connexis ; cellulis perdurantibus termi- 

 nalibua vel interjectis. 



Dmm.— Cell, vegetat. ^^^^W = -000166 ; cell, perdur. t^Uts" = -00033. 



Hab.^-ln terrestre, New Jersey, (Prof. Austin.) 



Terrestrial ; thallus expanded, irregular or orbicular, very thin, seruginous, small, membranousi 

 pellucid; filaments loosely interwoven, variously curved, joints globose or often elliptical, 

 mostly pellucid in the centre, loosely connected ; heterocysts terminal or interspersed. 



Remarhs. — Mr. Austin has kindly sent me the only specimens I have seen of this 

 species; they are labelled "Damp Ground, Sept." The fronds, which are often 

 aggregated, are very small and exceedingly thin, especially in their central por- 

 tions, where they are quite translucent; in form they are often circular, some- 

 times quadrangular, sometimes quite irregular. As to size, most of them are not 

 more than two lines in diameter, some three, or possibly five lines. The margins 

 are often reflexed and thickened, especially in the smallest fronds. Two kinds 

 of filaments are visible; 1st, those which I take to be in a perfected quiescent 

 state ; 2d, those which are in active growth. The former are composed of globose, 

 or more commonly elliptical joints, which are remarkable for the possession of a 

 central translucent, almost colorless spot, the endochrome apparently being arranged 

 in a ring around the outer part of the cell. This is, however, occasionally want- 

 ing. The filaments, which are in active growth, are very irregular in form, often 

 much broader than the others; their cells very irregular and sometimes fused 

 together into one mass. The measurements given in the diagnosis were taken 

 from the filaments of the first kind. 



6. Thallus indefinite expansus. 

 Thallus indefinitely expanded. 

 TX. Cesatii, Bals. 



N. terrestre ; thallo longe lateque expanso, gelatinoso-membranaceo, viridi-flavescente ; tricho- 

 matibus flexuoso-curvatis, sublaxe implicatis, pallide serugineis ; articulis sphfericis, laxe vel 

 arctius connexis ; cellulis perdurantibus spb^ricis, et interjectis et terminalibus. 



Diam.— Artie. .00016—0002; cell, perdur.— .00033". 



Syn. — N. Gesatii, Bals. Rabenhorst, Flora Europ. Sect. II. p. 115. 



Eah.—ln terrestre, Kansas (Prof. Parry) ; Texas (Prof. Ravenel). 



Terrestrial; thallus broadly and indefinitely expanded, gelatinous-membranaceous, yellowish- 

 green; filaments flexuously curved, rather laxly implicate, pale-greenish; articles spherical, 

 laxly or more closely connected ; heterocysts spherical, both interstitial and terminalibus. 



