THE GREEN AI.GAE OF NORTH AMERICA 153 



3. C. PUSILUM (Lyng.) Kjellinan, 1883, p. 318. Fronds 

 long, very slender at base of the stipe, widening slowly to the 

 clava, which is seldom over 60 p. diam. 



Forma TYPICUM Wittr. and Nordst., Alg. Exsicc., No. 457 ; 

 P. B.-A., No. 1126. Widening uniformly from base of stipe to 

 summit of clava ; stipe about twice as long as clava ; total 

 length up to 2 mm. ; greatest diam. about 60-70 p.. 



The typical C. pusillum has been found in America only in 

 Eastern Maine, where it forms velvety coatings on rocks about 

 half-tide level, unmixed with any other alga, and forming ex- 

 tensive patches on exposed rocks. 



Forma AMERICANUM Wille, in P. B.-A., No. 869. Stipe 

 5-10 times as long as clava, otherwise like the type. On rocks 

 near high water mark, at Marblehead, Mass., forming a coating 

 unmixed with other plants. 



Forma longipes (Foslie) nov. comb. ; C. longipes Foslie, 

 1881, p. n, PI. II, fig. 4; P. B.-A., No. 26. Division be- 

 tween stipe and clava usually marked, the lower part of clava 

 being about double the diam. of the summit of the stipe ; stipe 

 30-60 fj. diam., as long as clava ; total length up to 1200 yu,, larg- 

 est diameter 100 p.. 



This form is abundant along the coast of Maine, forming a 

 practically unmixed coating on rocks at half tide over consid- 

 erable stretches. In drying, the individual plants adhere in 

 such a way as to leave the transparent stipes exposed in minute 

 spots, giving the surface a mottled appearance, characteristic 

 and readily recognized, but not easy to describe. Something 

 of the same appearance is found in the other forms of these 

 species, but not to the same extent. 



Family 2. PROTOSIPHONACEAE. 



Unicellular, terrestrial, relatively large algae, multinucleate ; 

 chromatophore large and net-like ; cells often giving out color- 

 less prolongations, developing into normal cells at the end ; 

 sexual reproduction by zoogametes, asexual reproduction by 

 zoospores. 



Only one genus. 



PROTOSIPHON Klebs, 1896, p. 221. 



Frond unicellular, multinucleate, with net-like chromatophore 

 and many pyrenoids ; in form spherical, cylindrical, or irregu- 

 lar, with a slender, usually unbranched prolongation, penetra- 

 ting the moist ground on which it grows ; cells dividing vege- 



