MARINE ALG^E OF BEAUFORT, N. C. 415 



erect throughout, tapering very slightly toward the apices; sheath very thin, delicate, scarely visible; 

 trichomes light olivaceous (?), 5.0 to 8.3 mic. in diameter, slightly constricted at the septa toward apex, 

 scarcely so below, cells i to 3 (mostly 1.5-2) times as broad as long, the apical ones broadly dome-shaped 

 or almost hemispheric; heterocysts basal, usually single, rarely double, subspherical or ovoid, 5.0 to 

 6.6 mic. in diameter, or sometimes 8.3 mic. long, gonidia unknown. 



Endemic. 



Few patches of scattered filaments on Dictyota dichotoma dredged from the coral reef offshore from 

 Beaufort, N. C., August, 1914. 



This species will not be mistaken for any other occurring in this region. It has been found only 

 the one time noted. 



Family 3. SCYTONEMACE^E (Kuetzing) Rabenhorst. 

 Scytonematacez. Kirchner. in Engler and Prantl, 1900. p. 76. 



Trichomes composed of a single row of cells, one or more included within a sheath, 

 not ending in a hair at the apex; filaments branched, false branches formed by the 

 perforation of the sheath by the trichome which thereupon issues as one or two long, 

 flexuous branches, each developing a sheath of its own; sheaths homogeneous and 

 colorless, or lamellose and yellowish or brownish, firm, tubular, sometimes incrusted 

 with lime; heterocysts and gonidia variously distributed, sometimes lacking; multipli- 

 cation by means of vegetative division, hormogonia, and gonidia. 



Filaments usually forming tufted masses, sometimes matted or ragged layers. 

 Vegetative cells cylindrical or barrel -shaped, rarely spherical, apex hemispherical or semi- 

 ellipsoid, cell contents blue-green or sometimes violet or rose-red. Filaments nearly 

 uniformly thick at all points, and always with false branching; false branches always 

 occur in connection with the heterocysts, when these are present, going out either imme- 

 diately below a heterocyst or midway between two of these, the latter method giving a 

 pair of branches. Heterocysts present except in Plectonema, subspherical, oval, or 

 cylindrical, at the bases of the branches or intercalary in the filaments, single or several 

 adjoining, always attached to the inner wall of the sheath. 



About 150 species, mostly aerial or on moist earth or in fresh water, throughout the 



world. 



Genus Plectonema Thuret, ex Gomont. " 



Plectonema, Thuret, 1875, p. 375. 

 Plectonema. Gomont, 1893, tome 16, p. 96. 



Filaments free or forming feltlike masses, branched, false branches solitary or in 

 pairs; sheaths firm, colorless or rarely yellowish orange; trichomes frequently con- 

 stricted at the joints, apex of trichomes straight, very rarely attenuated, calyptra none, 

 heterocysts and gonidia none. 



Twenty-one species, mostly in fresh water, rarely on soil, few in salt water, America, 

 Europe, Asia. 

 Plectonema battersii Gomont. 



Plectonema baitersii, Gomont, 1899, P- 36. 

 Plectonema battersii. Forti. in De Toni. 1907, p. 495. 

 Plectonema battersii, Tilden, 1910, p. an. 

 P. B.-A. No. 1060. 



Plant mass blackish or brownish green; filaments elongate, flexuous, abundantly and repeatedly 

 branched, false branches usually in pairs, more slender than the main filaments; sheaths colorless, 

 somewhat thick in the main filaments; trichomes 2 to 3.5 mic. in diameter, constricted at joints, with 

 159321 20 4 



