THE GREEN ALGAE OP NORTH AMERICA 191 



marine species of Ulothrix, which are the only plants for which 

 it could be mistaken. 



4. S. SUBTILIS (Kiitz.) Klercker, 1896, p. 103; Hazen, 1902, 

 p. 162, PI. XXI, figs. 10-13; Ulothrix subtilis Wolle, 1887, p. 

 135, PI. CXVIII, figs. 9 and 10, in part; P. B.-A., No. 614. 

 Forming extensive, bright green, lubricous masses ; filaments 

 long, cylindrical, 5-6.5 yu, diam., rarely 8 //. ; cells 1-3 diam. long ; 

 wall thin, chromatophore elliptical, with a small pyrenoid ; fila- 

 ments showing little tendency to break up. Greenland, Me., 

 Vt. to Pa., Cal. Europe. 



Very common in spring, especially where water is running 

 over rocks ; also in watering-troughs and in pools ; less com- 

 mon at other seasons. 



5. S. FLACCIDUS (Kiitz.) Gay, 1891, p. 79, PI. XI, figs. 101- 

 106 ; Hazen, 1902, p. 164, PI. XXI, figs. 14-17 ; P. B.-A., Nos. 

 116, 1222; Ulothrix flaccida Wolle, 1887, p. 137, PI. CXVIII, 

 figs. 27-28. Filaments rather short, forming floccose or inter- 

 woven masses; cells 6-9.5 /" diam., somewhat swollen, %-\ 

 diam. long, occasionally up to 2 diam.; cell wall fairly thick ; 

 chromatophore broad, with a large pyrenoid. On wet rocks 

 and soil, and on the bark of trees. Mass., N. Y., Cal., and 

 probably generally distributed. Europe. 



Only slightly larger than .5". subtilis, but with cells usually 

 shorter, distinctly swollen, and with a thicker wall ; a plant of 

 moist places rather than submerged. 



6. S. FLUITANS Gay, 1893, p. CLXXIV, fig. i ; P. B.-A., 

 No. 759; Hazen, 1902, p. 165, PI. XXII, figs. 7-9. Filaments 

 yellowish green, crisped and interwoven, sometimes geniculate, 

 with a strong tendency to break up, 6.5-9 ^ diarn., cells 1-3 

 diam. long ; chromatophore large and thick, nearly concealing 

 the inconspicuous pyrenoid. Mass., N. J. Europe. 



In the two American localities this species occurs on smooth 

 rocks swept by rapid water from a cascade ; the filaments are 

 unaffected by the current, but when removed to quiet water 

 break up into individual cells in a very short time. 



7. S. RIVULARIS (Kiitz.) Hazen, 1902, p. 166, PI. XXII, 

 fig. 10-13; Ulothrix rividaris Wolle, 1887, p. 136, PI. CXVIII, 

 figs. 6-8, 29-33. Forming bright green tufts ; filaments some- 

 what geniculate but not easily breaking up, 8-n ^ diam., of few 

 cells ; giving out hooked rhizoidal branches ; cells 1-2 diam. 

 long, somewhat swollen ; chromatophore orbicular to rhom- 



