372 DR. SARAH M. BAKER AND MISS M. H. BOHLING ON 
Generally, the green alge persist with the Fucus, Enteromorpha, espe- 
cially, forming a common undergrowth in the Mersea marshes. Very shortly 
after the colonization of a mud-bank by Fucus, seedling halophytes begin 
to grow up through the dense algal vegetation, and so the mud becomes a 
salt marsh, and throughout its earlier stages, i.e. at the lower levels, the 
Fucus persists as an undergrowth. 
In many localities the ‘green and blue-green filamentous alge, always con- 
spicuous as sand- or mud-binders, in the earliest stages of colonization, form 
the only algal vegetation of large areas of salt marshes. Compare Gomont’s 
report on the saltings of Lorraine (Gomont, 1908, pp. 29-88), where Cyano- 
phyceæ, especially Lyngbia Aestuarii and Microcoleus ehthonoplastes, are the 
predominant algal vegetation, and no brown alge are represented at all. 
Ета. 18.— Еисиз vesiculosus megecad limicola. 
Showing vegetative sprouting from buried parts of the thallus, through an 
accreting mud-bank. 
But where the Fucoids enter into а salt marsh they naturally become the chief 
vegetation over the marsh surface, owing to their large size and. luxuriant 
habit, and the Cyanophyceæ and Chlorophyce are then restricted to mud- 
flats and stream-banks, where Fucus cannot obtain a footing, or else they 
may persist as a ground flora beneath the Fucus. 
(b) Brown Alge as Undergrowth. 
The most characteristic function of the marsh alow is that of a dense 
undergrowth around the phanerogams. The halophytes serve as anchorage 
and protection from excessive scour to the alge, and the ао, in their 
turn, form an incubation bed for the seedling halophytes, and also prevent 
undue evaporation from the marsh soil. The beneficial effect of an under- 
growth of Pelvetia upon Salicornia europea has been shown experimentally 
by Oliver (in Baker, 1912, p. 282), and no doubt a similar benefit is conferred 
by other alge, functioning as undergrowth. РІ. 29 shows an undergrowth 
of Ascophyllum nodosum ecad scorpioides with Aster. 
