48 SPECIES OF ALG^. 



b. Permanently attached, in rapid streams . . . fluitans, 145 



b. Not permanently attached {c). 



£. Diameter of filaments 13-15. 5;u . . . fontitMli, 144 



c. " " " 2S-33yU stagnale, 145 



c. " " " 36-40yU . . Horsfordii, 145 



30. VAUCHERIA, 

 I. KEY TO THE STERILE PLANTS. 



§ In salt or brackish water; mats velvety, feet in extent, 



Thurdii, 149 

 § In sweet water or somewhat terrestrial {a). 

 § Apparently terrestrial only (h). 



a. Filaments dichotomous, branches constricted at the base of the 

 divisions, often intermediately, .... . tuberosa, 154 



a. Filaments not constricted at the branching points {b). 



b. Stratum dense, pellucid below, creeping; terminal branches erect, 



clustered, often crooked . ... velutina, 153 



b. Stratum not pellucid below {c). 



c. Branches not clustered, vague. Thus far found only in California, 



hamata, 153 



c. Branches dichotomous or sparingly formed {d). 



d. Diameter of filaments loofx or more (e). 



d. " " " less than ioo/.t [g). 



e. Diameter 100 to 2oo/< (/). 



/. Diameter 125;.*; tufts dense, dark green . . geminata, 151 



/. " loo/t; tufts loose, expanding in all directions, 



aversa, 149 

 /. " ioo-2oo/t; dirty green or brownish; about limestone 



springs ... . . dichotoma, 149 



/. Diameter 1 8o-2ooyU, often hyaline; drying ash gray . pilus, 153 

 g. In turfy mats; filaments densely intricate; 50-75// in diameter, 



se7-icea, 150 

 g. In dense, intricate tufts; filaments dichotomous, 50// in diameter, 



geminata, 151 

 g. In loosely intricate clusters; filaments about 50/1 in diameter, 



sessilis, 151 

 h. Stratum thin, expanded, filaments about 50/* in diameter, 



Dillwynii, 150 

 h. " " densely interwoven, dark green . . terrestris, 153 



