22 
INTRODUCTION. 
IV. 
tation, and strongly resemble the efflorescent forms, like cauliflowers, seen so fre- 
quently in the sparry concretions of limestone caverns. Others, more perfect, 
become branched like corals ; and the most organised of the group, or the true 
corallines, have symmetrical, articulated fronds. This stony vegetation affords 
suitable food to hosts of zoophytes and mollusca, which require lime for the con- 
struction of their skeletons or shells, and it probably extends to a depth as great as 
such animals inhabit. 
When the same species is found at different depths, there is generally a marked 
difference between the specimens. Thus, when an individual plant grows either in 
shallower or in deeper water than that natural to the species, it becomes stunted or 
otherwise distorted. I have noticed in many species (as in Plocamium coccineum , 
Dasya coccinea , Laurencia dasyphylla , various Hypnece , and many others) that the 
specimens from deep water have divaricated branches and ramuli, and a tendency 
to form both hooks and discs or supplementary roots, from various points of the 
stem and branches. Sometimes the outward habit is so completely changed by the 
production of hooked processes and discs, that it is difficult to discover the affinity of 
these distorted forms ; and such specimens have occasionally been unduly elevated 
to the rank of species. 
When water of great depth intervenes, on a coast between two shallower parts 
of the sea, it frequently limits the distribution of species, acting as a high mountain 
range would in the distribution of land plants ; but in a far less degree ; as it is 
obviously easier for the spores of the Algae to be floated across the deep gulf, 
than for the seeds of land plants to pass the snowy peaks of a mountain. 
The intervention of sand, already alluded to, is a far greater barrier, because 
sandy tracts are usually of much greater extent than submarine obstacles of any 
other kind. To the prevalence of a sandy coast, in a great measure probably, is 
owing the very limited distribution of the Fucacece on the eastern shores of 
North America, where plants of this family are scarcely found from New York to 
Florida. Since the erection of a breakwater at Sullivan’s Island, S. C., many Algae 
not before known in those waters have, according to Professor L. R. Gibbes’s 
authority, made their appearance, but none of the Fucaceae are yet among them. 
In due time Sargassum vulgare will probably arrive from the south. 
Some attempt has been made to divide the marine flora into separate regions, the 
particulars of which I have detailed elsewhere.* In the descriptive portion of this 
work I shall notice the distribution of the several families, where it offers any 
marked peculiarity, and I shall at present confine myself to some remarks on the 
distribution of Algae along the eastern and southern shores of the United States ; 
here recording the substance of some verbal observations which I made at the 
Meeting of the American Association, held in Charleston, in March, 1850. 
EASTERN SHORES OF NORTH AMERICA. 
In comparing the marine vegetation of the opposite shores of the northern Atlantic, 
Manual of British Marine Algae, Introd., p. xxxvi. et seq. ed. 2. 
