.62 FRESH-WATER ALG^E OP THE UNITED STATES. 



Csespitose, mucous, mostly intermixed with various algae; filaments more or less curved; 

 branches mostly in pairs, elongate, simple, variously curved; internal filament partly dis- 

 tinctly articulate, partly not articulate, sometimes nioniliform, yellowish-green or ajruginous, 

 granular; joints mostly shorter than the diameter, sometimes muc.h longer, sometimes sub- 

 globose or strongly compressed; heterocysts single, subcylindrical ; sheaths distinctly lamel- 

 late, mostly reddish or yellowish-brown, but sometimes colorless, in branches hyaline, color- 

 less, or with a very faint yellowish tint, or sometimes brownish. 



Remarks. The specimens, from which the above description was drawn up, 

 were sent me by Professor Ravenel from South Carolina. The extremities of the 

 sheaths are either closed, or open. The branches are almost always in pairs, and 

 sometimes three or four are given off together, but this is not common. They 

 are often nearly or quite colorless; the main filament is generally a sort of 

 brown sometimes quite bright from the predominance of the yellow hue. 

 Although my specimens do not precisely agree with the descriptions of the 

 European S. calotrichoides, yet the disagreement does not seem sufficient or 

 sufficiently constant to separate specifically the two forms; the most important of 

 the differences is in the coloration of the sheaths and heterocysts, which in the 

 American plant are commonly, but not universally, respectively brownish and 

 greenish. 



The label, which Professor Ravenel has attached to some of the specimens, 

 reads, " In wet, boggy places, on rotten pine boards, Sept. 25, 1869." 



Fig. 2, pi. 6, represents a filament of this plant magnified 250 diameters. 



S. cataracta, WOOD. 



S. rupicola, caespitosum, fusco-atrum, longe et late expansum; trichomatibus flexuosis, flexili- 

 bus, fere*0.25" longibns, vage pseudoramosissimis, superficie tevibus; pseudoramis elongatis, 

 singulis, rarissime getninis, liberis, interdum fuscis, seepius hyalinis, apice plerumque truncatis 

 et rare nonnihil attenuatis et Sffipe barbais sed haud rubellis ; trichomatibus internis serugi- 

 neis, tenuissimis, plerumque distincte articulatis ; articulis diametro plerumque brevioribus, 

 sed interdum longioribus, ssepe sejunctis, stepe subglobosis ; vaginis crassis et firmis; cellulis 

 perdurantibus et basilaribus et iuterjectis, siiigulis, rarissime geminis. 



Diam. Trich. cum vag. plerumque. 00045"; max. .0011"; sine vag. max. .00013". 

 Syn. S. cataracta, WOOD, Prodromus, Proc. Am. Phil. Soc., p. 129, 18G9. 

 Hab. In flumine Niagara prope cataractam. 



S. forming on rocks an extended turf-like stratum of a brownish-black color ; filaments flexuons, 

 flexible, almost 0.25" long, irregularly branched, their surface smooth ; branches elongate, 

 single, rarely in pairs, free, sometimes fuscous, frequently hyaline, their apices generally 

 truncate, rarely somewhat attenuate, frequently provided with enlargements, never reddish ; 

 cytioplasm seruginous, very thin, generally distinctly articulate ; articles mostly shorter than 

 broad, but sometimes longer, frequently disjoined, often subglobose; sheaths thick and firm; 

 heterocysts both basal and interjected, single, extremely rarely geminate. 



Remarks. This species grows abundantly in the Niagara River, on the rocks 

 below the great cataract. It is really in little tufts, but these are in many cases 

 placed so closely as to form a broad turf-like coating to the stones. Often, however, 

 the tufts are in smaller patches, and are of sufficient length to wave with the 

 eddies and currents in the water. The branches are almost always given off 



