NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 241 



body of the vesicle, above into a long apicula vi^hich is often somewhat 

 flattened or even resembles a leaf- remnant ; receptacles known for both 

 antheridial, oogonial and intersex plants ; antheridial receptacles cylindri- 

 cal, once to several times branched, smooth except frequently for small, 

 scattered teeth, more often associated with leaves than vesicles in the in- 

 florescences ; oogonial receptacles little different in size and shape from 

 antheridial ones but with little or no evidence of denticulations, usually 

 associated with vesicles in an inflorescence in such a compact way that it 

 may be termed a heteroclyte cyme. 



This is a common species in the lower littoral and upper sublittoral at 

 many stations. E. F. Ricketts says that in April this species is the com- 

 monest one below the Padina Durvillaei belt at Puerto Refugio. 



D. 355, 357a, Punta Penasco, Feb.; Poindexter, March; J. 71, 

 Georges Island, April ; D. 476, Puerto San Carlos near Guaymas, Feb. ; 

 D. & R. 2914, Kino, Nov.; J. 2, Puerto Refugio, June; D. 551, cast up 

 at Agua Verde Bay, Feb. 



Sargassum Johnstonii f. gracile S. & G. 

 Plate 33, Figs. 3-16 



Setch. & Gard., 1924, p. 738, pi. 21, fig. 76. Sargassum Johnstonii f. lax- 

 ius S. & G., p. 737, pi. 21, figs. 75, 81. 



This form is like the species but more slender and lax throughout, 

 with fewer and longer, more stringy branches; leaves not much flattened, 

 usually filiform with relatively more abundant and conspicuous crypto- 

 stomata ; vesicles with long cylindrical apiculae. 



Growing in upper sublittoral or lower littoral : D. 340, Punta Pefias- 

 co, Feb.; M. 28, 28a, Guaymas; D. 63, Guaymas, Jan. 



II. The Lapazeamim Group 



Plates 34-37 



Plants from slender, short stipes, attached by an essentially paren- 

 chymatous, discoid, semirhizomatous holdfast; leaves ecostate, expanded, 

 unsymmetrical. 



Most members of this group are easily distinguished from other Gulf 

 species by their unsymmetrical, ecostate leaves. The group as a whole is 

 rather sharply defined. The members show close mutual relationship in 

 the gradation in size and shape of leaves and vesicles from Sargassu?n 

 Inpazcanum to the long-vesicled floating form of S. MacDougalii. 



Sargassum lapazeamim represents a small-leaved, short-vesicled spe- 

 cies found thus far at Guaymas, San Marcos Island, Tortuga Island, 



