THE BROWN SEAWEEDS OF THE SALT MARSH, 347 
indicate a new form which results from adaptation or a change in morphology 
due to a new habitat. Each of these marsh varieties is, then, an ecad. 
But there are certain definite modifications in habit, correlated with the 
marsh habitat, which distinguish all the marsh ecads very sharply from 
the numerous morphological varieties which have been recognised in the 
rock species, and these modifications are not only maintained through many 
vegetative generations but are common to all the species which inhabit salt 
marshes. 
For this reason we propose to group together all the salt-marsh ecads 
into one * megecad " which will define the general peculiarities due to the 
habitat. We shall call this the megecad “ limicola,” including in the term 
all the mud-dwelling Fucoids as distinguished from their saxicolous parents. 
This megecad limicola comprises two sections, the varieties of the salt-marsh 
formation and the varieties of the loose-lying formation, both of which, as 
we shall see later, are dominated by very similar physical conditions. 
The general characteristics distinguishing the megecad limicola for the 
Fucoideæ are :— 
(1) Vegetative reproduction. 
(2) Absence of a definite attachment disc. 
(3) Dwarf habit. 
And, applicable to the salt-marsh section only :— 
(4) Curling or spirality of the thallus. 
At least three of these characters should be present to justify the inclusion 
of a variety under the “ megecad” limicola. As was before stated, Fucus 
spiralis v. папа and Ascophyllum nodosum v. minor, although they occur 
on marshes, cannot be considered as true marsh forms, but are practically 
identical with the corresponding saxicolous varieties. 
The following Table has been drawn up to summarize the results brought 
forward in this section. For the sake of comparison, the loose-lying forms 
of F. vesiculosus and also the form of F. inflatus, signalised by Rosenvinge 
and later by Jgussen as forming a dense matted growth of twisted fronds 
in lagoons of calm water in Greenland, have been included, although the 
species are not British. The tabulated descriptions apply always to the mud 
forms and not the parent species. 
