THE BROWN SEAWEEDS OF THE SALT MARSH. 327 
referred by other writers (Arcichovskij, 1905; N. Svedelius, 1901, p. 85) to 
degeneration produced progressively by long-continued vegetative repro- 
duetion under these conditions. Although inherent effects of this kind have 
undoubtedly some influence in altering the habit of such plastic organisms 
as the Algæ, the evidence we have collected goes to show that the most 
striking morphological peculiarities of the salt-marsh forms are evoked as a 
direct response to the new physical and chemical conditions of the habitat. 
It was necessary, however, before any idea could be obtained of the change 
in morphology produced in any one species under the new conditions, to 
establish very definitely the genetic relationships between the various salt- 
marsh forms and the corresponding rock species. Аз Cotton (1912, p. 125) 
has already pointed out, the nomenclature, especially of the dwarf forms of 
Fucus, so common on salt marshes, is in a state of chaos, no two authors 
agreeing as to the status, form, variety, or species, of these peculiar plants. 
The first part of this paper will be devoted to a consideration of the syste- 
matic status and relationships of the British Fucoids which have been 
reported from salt marshes, and will include a description of a new salt- 
marsh variety, derived from Fucus ceranoides, found at Keyhaven, Hants. 
The second part of the paper will deal more particularly with the relations 
between the physieal faetors operating in the salt marsh and the morpho- 
logical peculiarities of salt-marsh Fucoids ; while the third part will give a 
short account of the relative distribution of the Fucoids and the other Alga 
of the salt marsh, and their special functions in the autonomy оЁ the marsh, 
in certain areas which have come under our own observation. 
PART 1. 
SYSTEMATIC POSITION OF THE MARSH Fucoips. 
THE Rock Fucorps. 
On the coasts of the British Isles we have six common species of the 
Fucoideæ characteristic of the littoral region of sheltered rocky shores ; 
these are given in descending order of altitude :— 
Pelvetia canaliculata (L.), Decne & Thur. 
Fucus spiralis, L. (=platycarpus, Thur.). 
Ascophyllum nodosum (L.), Le Jol. | Relative height varies 
Fucus vesiculosus, L. } in different localities, 
Fucus serratus, L. 
Also Fucus ceranoides, L., characteristic of brackish water. 
On exposed coasts Himanthalia lorea replaces Ascophyllum (see Cotton, 
Clare Island, p. 38). 
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