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



The following arrangement from Rabenhorst's Flora Algarum, 

 will be useful in their identification. 



FILAMENTS COLLECTED IN FLOATING MATS, MORE OR LESS LAXLY 



INTRICATE. 



A. At first attached as tufts, afterwards floating as mats. 



a. Cell contents not spirally disposed. 



Fruiting cells not terminal. 



1. C. FRACTA, Kg. Cell-membrane smooth, articulation more or 

 less swollen. 



b. Var. gossypina, Kg. 

 c. Var. horrida, Kg. 

 d. Var. rigidula, Kg. 

 e. Var. viadrina, Kg. 



C. OLIGOCLONA, Kg. j" Articulations not swollen, cylindrical, 

 C. FLOTOWIANA, Kg. ( filaments long, sparsely branched. 



3. C. CRISPATA, Kg. Cell-membrane delicately plicate-striate. 



b. Var. vitrea, Kg. 



c. Var. brachyclados, Kg. 



B. Tufts attached for the whole life. 



b. Cell-contents vaguely disposed in lax spirals. 



fruiting cells terminal or subterminal. 



4. C. CANALICULARIS, Kg. Cell-membrane even ; branches con- 



nate at the base. 



5. C. GLOMERATA, Kg. Branches not connate at the base. 



b. Var. mucosa, Kg. 

 c. Var. rivularis, Rab. 

 d. Var. simplicior, Rab. 

 e. Var. subsimplex, Rab. 

 f. Var. clavata, Wolle. 

 g. Var. pumila, Bail. 



6. C. FLUITANS, Kg. Filaments long, sparsely branched. 



7. C. FLAVESCENS, Ag. Cell-membrane plicate. 



8. C. ^EGAGROPILA, Kg. Filaments radiating from a common 



center, aggregated in a more or less spongy globe. 



9. C. BRACHYSTELECHA, Rab. Doubtful species. 



CLADOPHORA FRACTA, Kg. 



Filaments irregularly branched, in clusters or turfy 

 masses of dark green color. Zoogonidia are developed in 



