Clare Island Survey — Murine Algae. 15 79 



on the same marsh. In the Clew Bay district the substratum consists of 

 peat, or of a loamy soil derived from the boulder-clay ; patches of mud also 

 occur. With the exception of the dwarf Fucus, most of the algae associations 

 described below occur on each of these types of ground. The mud-flora is 

 the most distinct, and where soft it differs markedly ; but otherwise the 

 nature of the substratum does not appear to exert a great influence in this 

 particular district. With a detailed study certain differences would doubtless 

 be detected. The vegetation of the mud-patches of the salt-marsh approaches 

 on the one hand that of the mud-banks of the tidal streams, and on the other 

 that of the mud-flats below high-water mark. Several of the salt-marsh 

 species lie on the ground, or on other vegetation ; but B'ostryehia is epiphytic 

 on Statice, Atriplex, and similar plants ; consequently the presence of these 

 algae is in part dependent on the character of the phanerogamic vegetation. 

 But the converse is also true. Hill ('09, p. 102) and Baker ('12) have 

 shown the importance of- the Bhizoclonium covering in connexion with the 

 germination of Salicornia seeds ; and the same matted growths doubtless 

 protect seedlings and young plants from excessive insolation. 



The Olew Bay salt-marshes agree well as to their flora with the general 

 description given above. The four types of vegetation distinguished were : — 



1. Bhizoclonium association. 



2. Fucus vesiculosus var. muscoides association. 



3. Bostrychia-Catenella vegetation. 



4. Vegetation of vertical banks: 



The areas specially explored were those on or near Annagh Island, and 

 below the hotel at Mulranny. Small patches of ground supplying similar 

 vegetation were also examined in Bellacragher Bay and at Leenane. 



Bhizoclonium Association. 



Rliizocloiiium ripariwm is the dominant species in the felt-like sheets of 

 green algae which are often so conspicuous on the salt-marsh. These sheets 

 are found typically on bare soil (sand, loam, or peat), and at Mulranny are 

 continuous with the Rhizoclonium association, which occurs on the sand from 

 half -tide level and above. On the marsh, Bhizoclonium is also abundant in 

 shallow pools, and it invades (especially in warm, damp weather of spring) 

 areas colonized by phanerogams. When Bhizoclonium alone is present, the 

 growth is light-green ; but when, as is often the case, Enteromorpha occurs in 

 addition, the colour is deeper, and does not turn pale to the same extent on 

 drying. Brown and black streaks in the felt indicate the presence of 



