190 FRESH-WATER ALG^J OF THE UNITED STATES. 



that filaments of this kind are more or less frequently intermin- 

 gled with UlothriXj Cylindrocapsa, Conferva, and others. The cell 

 membranes soften and diffuse, producing wide colorless envel- 

 opes, such as were made characteristic of this genus. Compare 

 descriptions of these genera, and particularly the illustrations. 



Plate CLXXXVII, figs. 10-23. 



Genus 54, TETEASPOEA, Ag. 



Cells green, spherical, contained in a thick, gelatinous or sub- 

 membranous thallus, which in the beginning is short, sack-like, 

 afterwards expanded. Cells more or less by twos or fours, as 

 they divide in one or more directions ; afterwards scattered. 

 Tegument thick, very rapidly diffluent into a homogeneous 

 mucus. Zoospores are developed singly, one in a maternal cell. 



These gelatinous structures are of questionable value, as true, 

 fully developed plants ; they are evidently a mere condition of 

 growth, but having hitherto failed to detect, with certainty, their 

 relationship, they are allowed to retain their nominal positions. 



Older thalli often contain developing forms of filamentous 

 plants, such as Scytonema, Sirosiphon, Hapalosiphon and others. 

 One variety T. gelatinosa, as found several times, two or three 

 years apart, contained filaments of OsciUaria cruenta, Grun., 

 scattered through the very large gelatinous masses. 



Other varieties appear to be more nearly related to Spiro- 

 gyra and other Chlorophycece. 



TETRASPORA CYLINDRICA, Ag. 



Thallus attached, attains a length of 6-10 inches ; 2-10 // 

 thick, tubular cylindrical, simple, ends tapering to a fine 

 point, rather firm, gelatinous, dull or brighter green color. 



Diameter of cells about 16 /*. 



Syn. Viva cylindrica, Wallenbg. 

 Trenches of spring water. 



Plate CLXY, figs. 7, 8, T. cylindrica half the natural size, 

 and cells magnified. 



TETRASPORA BULLOSA, (Eoth.) Ag. 



Thallus rnernbranaceous, saccate, obovate, sinuate, bullose, 

 one to six inches long, dark green, smooth or more or less 

 verrucose; cells nearly spherical, geminate, or quaternate, 

 crowded, granular. 



Diameter of cells, 6-12 /*. 



