PH^EOPHYCE^E 55 



currents, &c., play a very important part in producing 

 mere growth forms which abound in common species 

 like F. vesiculosus. 



Geographical Distribution. The Fucacece occur in all 

 seas, those of the north temperate and arctic regions 

 differing considerably from those of the south tem- 

 perate and antarctic. Each possesses peculiar types, 

 while the intervening tropical zone has also its charac- 

 teristic genera. The south temperate zone is richer 

 in generic types than any other region, while the 

 tropical zone (especially the south sub-tropical) with 

 comparatively few genera furnishes the most species. 

 Among the southern temperate generic types with 

 few species there are Durvillea, Sarcophycus, Myrio- 

 desma, Carpoglossum, Hoi^mosira, Marginaria, Scyto- 

 thalia, Carpophyllum,, Landsburghia, Xiphophora, and 

 Phyllospora, Of small genera represented in both 

 northern and southern temperate zones there are 

 only Pycnophycus and Halidrys. The peculiarly 

 northern genera are Himanthalia, Ascophyllum , 

 Pelvetia, Fgrcgia, Coccophora, and Fucus. (F. 

 vesiculosus has been recorded from the Cape 

 and Australia, but the record is open to 

 question.) Cystophora has a remarkable distribu- 

 tion, its twenty or more species being limited to 

 warm Australian seas. Sargassum, which reaches its 

 maximum in the same region, contains about 150 

 species, but of a more distinctly tropical character 

 than Cystophora. Cystophyllum has ten species, 

 mostly sub- tropical, while Cystoseira, with thirty 

 species, has a wider range into temperate seas. 

 Turbinaria, with a few species, is strictly tropical. 



