THE GREEN ALGAE OF NORTH AMERICA 359 



diam. long, more or less matted at the base by descending 

 rhizoidal filaments, slightly smaller than the main filaments. 

 On various algae. Greenland to Conn. Europe. 



A spring plant, forming very regular rounded tufts on vari- 

 ous algae, the tufts becoming detached as the plant matures. 

 It is noteworthy as having only one nucleus to a cell, while as 

 far as observed all other species of Spongomorpha and Clado- 

 phora have normally two or more nuclei. It is possible that 

 some of the Alaskan species may also be uninucleate, but no 

 certainty can be had from dried specimens. On the other hand, 

 single uninucleate cells are occasionally, though rarely, found 

 in other species ; and as apart from this character this species is 

 in everything conformable to Spongomorplia, it does not seem 

 necessary to institute a separate genus for it. 



Var. UNCIAUS (Fl. Dan.) Kjellman, 1883, p. 306; Cladophora 

 imdalis Harvey, 1846-51, PI. CCVII ; 1858, p. 77; C. lanosa 

 var. undalis Farlow, iSSi, p. 51 ; P. B.-A., No. 77. Tufts ir- 

 regular in outline, growing on rocks, not floating away when 

 mature, but persistent in a coarse and faded state. Me. to 

 Conn. Europe. 



4. S. ARCTA (Dillw.) Kiitzing, 1849, p. 417; Cladophora 

 arcta Harvey, 1846-51, PI. CXXXV ; 1858, p. 75; Farlow, 

 iSSi, p. 50; P. B.-A., Nos. 224, 815. Fronds rich green, in 

 dense fastigiate tufts, up to 15 cm. high; filaments erect, stiff, 

 60-100 ju. diam. at tips, cells 4-6 diam. -long ; below smaller, cells 

 i Y-2. -3 diam. long ; much branched, branches erect or appressed, 

 obtuse orclavate ; rhizoidal descending branches 40-60 /u, diam., 

 cells 2-6 diam. long, firmly matting together the lower part of 

 the tuft. On exposed rocky shores in spring. Greenland to 

 N. J. ; Alaska to Wash. 



A common plant, the rounded rich green tufts being very 

 handsome while the plant is young ; later it becomes coarse 

 and faded.* 



Forma conglutinata nov. comb. ; Cladophora arcta forma 

 conglutinata Collins in Setchell and Gardner, 1903, p. 225. 

 Filaments adhering in pointed, Symploca-like tufts ; patent 

 acute branches occasionally found at the base of older plants. 

 Alaska to Wash. 



*Var. penidlliformis Foslie in Wittr. and Nordst., Alg. Exsicc., No. 

 613, a rather slender form with terminal sporangia, is doubtfully re- 

 ported from Greenland, Roseuvinge, 1893, p. 908; Jonsson, 1904, p. 49- 



