IY. 
INTRODUCTION. 
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 
Algm 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 
seven out of eleven European species are found in the Mediterranean. 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 and 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. Alsidium tri- 
angidare , Digenia simplex, Acantliopliora , Amansia multfida and other common 
West Indian Rhodosperms are abundantly cast ashore. Sargassum mdgare and 
bacciferum ; 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 Caulerpaceae. 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) ; TJdotea ; Halimeda ; 
Acetabularia ; Anadyomene ; Dictyo splicer ia ; Chamcedoris ; Dasyclaclus ; Cy- 
inopolia , 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 meat 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 Ptelesserice , (D. involvens , and J). tenuifolia) 
both belonging to the hypophyllous section, are specially worth notice. These 
were very plentiful in the beginning of February, but soon disappeared. Two 
Bostrychiae ( B . Montagnei , and B.Jilicula , MS.J and a Catenella were found on the 
