254 FRESH-WATER ALG^ OF THE UNITED STATES. 



sparsely branched ; branches mostly single, elongated. 

 Articulations rather distinct, not constricted; *-l<j times as 

 long as broad ; dull aeruginous. Sheath usually close and 

 colorless, rarely yellow or brown, not lamellate. 



Diameter, including sheath, 9-16 //. 



Found this species particularly abundant on Anastatia 

 Island, St. Augustine, Florida. Parts subject to an occa- 

 sional overflow by the tides were black with scab-like, black 

 crusts, composed of Nostoc communis and this Scytonema; 

 had a horn-like character when exposed to the sun and dried, 

 but when soaked in water soon became soft and gelatinous. 

 Could not trace the relationship between the Nostoc and the 

 Scytonema, but evidently they are very closely related. 



SCYTONEMA CINCINNATUM, Thlir. 



Usually forms dark green, or brown floating mats, with 

 filaments much interwoven. Vegetative cells short, often 

 contracted at the margins, three to six cells to a diameter ; 

 contents aeruginous. Heterocysts short, ellipsoidal or glo 

 bose, single or two (or more) in series of golden yellow 

 color ; diameter the same as the cells. Sheaths primarily 

 thin and colorless, later yellow or brown, and thicker. 



Diameter of internal filament. 14-18 // ; sheath 14.5-25 /-/. 



Syn. I/yngbya cincinnatum, Kg. ; Chrysostigma cincinnatum, Kirch. 



Inasmuch as this plant occurs in masses without branches 

 and without heterocysts, it justly represents Kutzing's form, 

 a Lyngbya ; and again in simple filaments with heterocysts, 

 it agrees with Kirchner's Chrysostigma, but it is found also 

 as described and illustrated. The different forms occur at 

 different seasons of the year, evidently the same plant. 



Plate CLXXXV, figs. 8-10 ; this specimen from a small 

 pond, near Bethlehem, Pa. Have the plant also from the 

 West and South. 



SCYTONEMA NOTARISII, Menegh. 



Stratum thin, filaments loosely interwoven, brown tinge ; 

 trichomes subsimple ; sparsely single and twin branched ; 

 internal filaments bright or duller aeruginous ; articulations 

 commonly indistinct, equal or half a diameter in length, 

 sometimes torulose : filaments primarily attenuated, sheath 

 multilamellate dissolving into fibrillae. Heterocysts rarely 

 observed. 



Plate CLXXXIV, figs. 1, 2, 3, normally developed plants ; 

 figs. 4, 5, the primary growths ; figs. 6-9, younger forms 



