NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 249 



eral habit erect and compact, not lax, internodes very short ; vesicles spher- 

 ical, smooth, 3-4.5 mm. in diam. ; receptacles (oogonial) 1-3 times 

 branched, -| cylindrical, somewhat spiny. 



Type: D. 686a, growing attached to cobblestones on rocky south 

 shore of Tiburon Island, July 17, 1940. 



It is unfortunate that most of the specimens of this collection were lost 

 on the return open-boat voyage to the mainland. Only a single plant lack- 

 ing the holdfast was saved. Field notes, however, verify the recollection 

 that the holdfast of this species is as described above, and this is substanti- 

 ated by a mature specimen with holdfast among J. Wyatt Durham's mate- 

 rial. These specimens are from a bay 10 miles N.W. of Guaymas, Oc- 

 tober 30, 1940. They agree well with those from Tiburon Island, and 

 represent fully mature plants with abundant receptacles. 



D. 158, Tiburon Island, Jan.; D. 463, San Esteban Island, Feb. 

 (probably this species but has undulate leaves) ; M. 18, 25, Eureka (per- 

 haps the same). Herb. AHF no. 15. 



IV. The Herporhiziim Group 



Sargassum herporhiziim and S. Brandegeet form a compact, easily 

 recognizable group because of the outstanding features of their attach- 

 ment organs. In both species attachment of adult plants is by means of 

 loose, spreading rhizomes which grow around pebbles and through the 

 generally loose substratum upon which the plants are found. When basal 

 parts are present, these plants need not be confused with species of other 

 groups, for this character together with the absence of conspicuous cryp- 

 tostomata distinguishes them readily. 



Sargassum herporhizum S. & G. 

 Plate 40, Figs, 1-12 



Setch. & Gard., 1924, p. 739, pi. 20, f^gs. 69-71. 



Only two collections of this species are thus far known: J. 72 from 

 Georges Island, April, and J. 55, San Pedro Martir Island, April. These 

 plants are distinct from S. Brandegeei in their smaller leaves whose mar- 

 gins are entire or only sparsely denticulate. S. Brandegeei is characterized 

 by very bold dentations of the margins. 



Sargassum Brandegeei S. & G. 

 Plate 40, Figs. 13-26 



Setch. & Gard., 1924, p. 736, pi. 21, fig. 79. 



Plants attached primarily by a parenchymatous disk, but branching 



