IV. INTRODtrCTION. 27 



strongly marked province, strikingly contrasting in vegetation with the East 

 Coast, comprised in the three regions already noticed. As yet the Keys have 

 been very imperfectly explored, and we are almost unacquainted with the marine 

 vegetation of the main land of Florida, Alabama, Louisiana, and Texas. Of 130 

 species which I collected at Key "West in February, 1850, scarcely one eighth are 

 common to the east coast, seven-eighths being unknown on the American shore 

 to the north of Cape Florida. With this remarkable difference between the 

 Algaj of the Keys and those of the East Coast, there is a marked affinity between 

 the former and those of the South of Europe. The marine vegetation of the Gulf 

 of Mexico has a very strong resemblance to that of the Mediterranean Sea. 

 Nearly one third of the species which I collected are common to the Mediterra- 

 nean. Several of them straggle northwards along the coast of Spain and 

 France, and even reach the south of England ; but scarcely any of these are seen 

 on the East coast of America. We may hence infer that they are not conveyed 

 by the gulf-stream. My collection at Key West included 10 Melanosperms, 5 of 

 which are common to the Mediterranean ; 82 Rhodosperms, 25 of which are 

 Mediterranean ; and 38 Chlorosperms, of which 10 are Mediterranean. Besides 

 these identical species, there are many representative species closely allied to Medi- 

 terranean types. This resemblance is clearly shown in the genus Dasya, of which 

 seveii out of ela^en European species are found in the ]\Iediterranean. At Key 

 West I collected eight species of this beautiful genus. Among these, seven were 

 new, and the eighth {D. elegans) is found along the whole eastern coast of North 

 America. Three-fourths perhaps of the masses of seaweed cast ashore at Key 

 West belong to Laurencia, of which genus several species arid innumerable puz- 

 zling varieties are profusely common. A fine Hypnea (H. Wurdemanni, MS.) 

 one of the most striking species of the genus, is also abundant. Alsidlum tri- 

 angidare^ Digenia simplex, Acanthophora, Amansia midtjida and other common 

 West Indian Rhodosperms are abundantly cast ashore. Sargassum vidgare and 

 hacciferum ; Padina Pavonia ; Zonaria lobata ; and sundry Dictyotce are charac- 

 teristic melanosperms. But this region is chiefly remarkable for the abundance 

 and beauty of its Chlorosperms of the groups Siphonacece and Caulerpacece. Ten 

 species of Caiderpa were collected, some of which are of common occurrence, 

 and serve for food to the turtles, which, in their turn are the staple article of 

 diet of the islanders. Penicillus (at least three species) ; Udotea ; Hcdimeda ; 

 Acetahularia ; Anadyomene ; Dictyosphcerla ; Chamcedoris ; Dasycladus ; Cy- 

 mopolia, and others, some of which are West Indian, some Mediterranean, are 

 evidence of the high temperature of the sea round the Keys. Many of the 

 plants obtained by me at Key West were cast up from deeper water when the 

 south wind blew strongly, and were not seen at any other time. A visitor, 

 therefore, in the hurricane months, would probably obtain many which escaped 

 me. Among the new species two Delesserice, (D. involvens, and 2). tenidfolia) 

 both belonging to the hypophyllous section, are specially worth notice. These 

 were very plentiful in the beginning of February, but soon disappeared. Two 

 Bosfrychice (B. Montagnei, and B.filicida, MS.J and a Catenella were found on the 



