NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 239 



2. Plants usually lax, with -\- — long internodes and 



-\ long lateral branches ; color brown ; base so far 



as known of coarse, short, woody rhizomes. 



a. Receptacles spinose or terminally dentate in both 

 sexes ; stems strongly muricate in oogonial plants . 

 S. horridum 



b. Receptacles smooth or nearly so in both sexes; 

 stems usually smooth S. sinicola 



B. Herporhizum group: cryptostomata absent or inconspicu- 

 ous on leaves of upper parts of plants; vesicles apiculate 

 (see also S. sinicola for some specimens) ; holdfasts of long, 

 loosely developed rhizomes. 



1 . Leaves dentate to very strongly so ; dentations more or 



less evenly spaced S. Brandegeei 



2. Leaves slightly and irregularly dentate or merely with 

 uneven margins ; plants drying very dark . S. herporhizum 



I. The Johnstonii Group 



Plates 32, 33 



Leaves ecostate, very slender, expanded to filiform; branching loose, 

 secondary mostly bifarious; vesicles elliptical, with long apiculae or 

 linear, foliar extensions ; cryptostomata usually frequent. 



The plants of this group are especially distinct from all others as re- 

 gards leaf-structure. The very slender, flattened to cylindrical leaves 

 give the plants a delicate, stringy appearance. They bear fairly numerous, 

 large cryptostomata which appear like eruptions on the surface. These 

 characters are generally reliable, especially when combined with the 

 elliptical vesicles which are almost universally tipped with a medium to 

 long apicula or flattened, linear, leafy extension. Sometimes the vesicles 

 are slender and the apicula is several times as long as the bladder. More 

 commonly the apicula and bladder are of about equal length. 



Antheridial and oogonial specimens are present in the collections, but 

 the receptacles are not markedly different, showing about the same degree 

 of branching and no recognizable difference in diameter. The antheridial 

 receptacles frequently have, however, a noticeable denticulation of the tips 

 and the surface, while thus far all oogonial receptacles have been found 

 to be smooth. The specimens available show to some degree evidence of 

 the more general association of vesicles with oogonial "inflorescences" 

 (Setchell, 1937) and of modified leaves with antheridial "inflorescences" 



