THE GREEN ALGAE OF NORTH AMERICA 343 



often be very puzzling. The angular main stem and the pecti- 

 nate terminal ramuli are the only constant marks to distinguish 

 it from other species of the same general dimensions. It seems 

 to be common from Massachusetts to Nova Scotia, both on ex- 

 posed shores and in bays ; more than most species of Cladophora 

 it thrives in places where it is quite out of water at low tide. 

 Several forms occurring on the New England coast have re- 

 ceived names. 



Var. VADORUM (Aresch.) Collins, 1902, p. 122; C. gracilis 

 var. tennis Farlow, 1881, p. 55 ; C. vadorum Wittr. and Nordst., 

 Alg. Exsicc., Nos. 1045, 1046. Filaments more slender than 

 in the type, 40-100 /a, cells 4-8 diam. long. Forming loose, 

 floating masses in the sublitoral zone, N. S. to N. J. Europe. 



Forma ELONGATA Collins, 1902, p. 122 ; P. B.-A., No. 725. 

 Frond stretching out on the surface of shallow water to a length 

 of a meter or more ; very glaucous green ; branches distant and 

 very erect. In shallow warm pools where there is a definite 

 steady current ; coast of Maine. 



Forma EXPANSA Farlow, iSSi, p. 55, as variety; P. B.-A., 

 No. 981. Frond soon detached, forming loose floating masses, 

 irregularly branched. Tide pools, coast of Maine and Massa- 

 chusetts. Forming floating masses, similar to C. cxpansa, but 

 not so dense. 



Forma SUBFLEXUOSA Collins, P. B.-A., No. 1530. Fronds 

 shorter than in the type, branching dense, branches flexuous. 

 A somewhat reduced form of shallow rock pools in northern 

 New England. 



This form appears to originate in pools where the water is 

 shallow, and there is no current ; where the water is shallow 

 and a current runs through when the tide is out, forma elongata 

 is produced. 



Forma australis n. f. Filaments less sharply angular ; 

 branches of all orders more patent. The common form south 

 of Cape Cod ; the opposite extreme from forma elongata, but 

 connected by every gradation. 



22. C. HIRTA Kiitzing, 1845, p. 208; 1854, PI. I, fig. 2 ; P. 

 B.-A., No. 726. Fronds 20-30 cm. high, stiff and harsh ; fila- 

 ments 150-200 /j. diam. at base, dull green, much or little 

 branched ; all set throughout or frequently with short, subacute, 

 more or less secund ramuli ; cells 2-4 diam. long, rarely some- 

 what more. In rather exposed places, Greenland to Long 

 Island Sound, and probably extending farther south. Europe. 



