238 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 3 



plants are placed under the four natural groups, each designated by the 

 name of the principal or most expressive species of the group. 



A considerable reduction in the number of species proposed by Setchell 

 and Gardner has been necessary, as well as the addition of three new ones. 

 From the specimens at hand in 1924 these authors were largely justified 

 in proposing the names they did. The material was often fragmentary, the 

 importance of the sexual nature was not so well understood as at present, 

 and little or nothing was known about the native habitats of the various 

 species or of seasonal disturbances. The present collections and records 

 help considerably toward clearing up some of the problems surrounding 

 this genus as it occurs in the Gulf, but the work is still in a preliminary 

 state. 



Key to the Species of Sargassum in the 

 Gulf of California 

 I. Leaves without a midrib (sometimes dimly costate in S. John- 

 stonii and S. lapazeanum) 



A. Johnstonii group: leaves very narrow, semiterete to flat- 

 tened (branching usually abundant, loose, spreading; ves- 

 icles elliptical, long-apiculate ; cryptostomata usually fre- 

 quent) S. Johnstonii 



B. Lapazeanum group : leaves expanded, asymmetrical. 



1. Vesicles mostly long-apiculate .... 5. acinacifolium 



2. Vesicles with foliaceous crest or extension 



a. Vesicles mostly only cristate ; upper leaves less than 



1 cm. long S. lapazeanum 



b. Vesicles with prolonged foliaceous extension; up- 

 per leaves large, more than L5 cm. long. 



( 1 ) Lower leaves usually less than half as long as 

 broad S. asymmetricum 



(2) Lower leaves almost as broad as long . . . 

 S. MacDougalii 



IL Leaves with a midrib 



A. Sinicola group: cryptostomata abundant and usually con- 

 spicuous on leaves of upper parts of plants ; vesicles mostly 

 spherical; known holdfasts parenchymatous or of short, 

 coarse rhizomes. 



1. Plants not lax, with short internodes and short lateral 

 branches ; color dark gray-brown ; base a solid paren- 

 chymatous disk or cone S. Camouii 



