236 FRESH-WATER ALG.E OF THE UNITED STATES. 



Family XVIILNOSTOCACE^E. 



Filamentous, simple or rarely with spurious branches, fur- 

 nished with heterocysts ; involved in a copious gelatin, more or 

 less firm or diffluent. The plants of some of the genera develop 

 spores, and are provided with heterocysts ; the former, usually 

 dark green, granular ; the heterocysts yellow or lighter or darker 

 yellowish brown, or nearly colorless, almost devoid of cytio- 

 plasm; sometimes they are terminal, sometimes interstitial, 

 between vegetative cells. The spores divide after a period of 

 rest, before or after the rupture of the cytioderm, and then ger- 

 minate and reproduce. The function of the heterocysts is not 

 determined. 



The Family NOSTOCACE^; may be divided into the following 

 five sections : 



I. BIVULARIEJE. 



II. SCYTONEME^. 

 III. SlROSIPHONE^. 



IV. NOSTOCE^;. 



V. OSCILLARIE^E. 

 SECTION I. RIVULARIE^E. 

 Genm 81, CALOTHEIX, (Ag.) Thur. 



Filaments rather rigid, nearly straight, branched; branches 

 spurious, being younger trichomes, agglutinated at the base and 

 part of their length to the parent stem, terminating at the apex 

 in a delicate hair-like extremity. Heterocysts normally present, 

 usually at base of branches ; often fasciculately branched ; grow- 

 ing in small tufts, or forming a light turf of indefinite extent. 



CALOTHRIX ORSINIANA, Thur. 



Forming a pulviuate stratum, about 40 yu in thickness, 

 dark brown, or reddish brown, lubricous, opaque ; trichomes 

 elongated, branches of nearly equal thickness, cuspidate at 

 the apex or obtuse, distinctly articulate ; sheaths thick, 

 smooth or lamellate, light golden brown. Trichomes with 

 sheath, 20-25 //; without sheath, 10-13 ^t. 



Syn. Scytonema cirrhosum, Berk.; Coenocoleus cirrhosus, Berk.; 

 Schizosiphon cateractce, Naeg. 

 On submerged stones, Florida. 



The measures quoted by Kirchner and by Cooke are less 

 than given above, but otherwise the description seems to 

 indicate a similar plant. 



Plate CLXYIII, figs. 1, 2. 



