15 80 Proceedings of the Royal Irish Academy. 



Cyanophyceae ; in Clew Bay usually Lyngbya confervoides and L. majuscula 

 respectively. 



The Ehizoelonium association is more general in some localities than in 

 others, and varies considerably according to the time of the year. Where 

 bare soil is scarce the growth is scanty ; where plentiful the felt is, except 

 in spots where strong tidal action obtains, usually abundant. In spring and 

 early summer Rhizoclonium, Percursaria, and Enteromorpha spp. are very 

 luxuriant; later in the season Cyanophyceae develop, and the felt-like 

 growth, as a whole, is not so extensive. The following species compose the 

 association in its wide sense : — 



Ehizoelonium riparium, dom. Lyngbya majuscula, Lab. 



Enteromorpha torta, /. L. confervoides, Lab. 



E. Ealfsii,/. Cladophora fracta ] 



Percursaria percursa, ab. Chaetomorpha linuml* 11 snai l° w 



Pylaiella litoralis, /". Capsosiphon aureolusj 

 Lyngbya aestuarii Lab. 



With certain weather-conditions the Ehizoclonium-felt is partially 

 destroyed. After a high tide, for instance, with a strong S.W. wind, much 

 of the growth at Mulranny is rolled up into rope-like masses ; whilst sheets 

 2 or 3 yards square have been observed deposited on the Glycerin maritima 

 sward, having been lifted bodily out of the shallow depression in which they 



Fucus vesiculosus var. muscoides Association. 



The carpet formed by this remarkable dwarf Fucus occurs above the 

 uppermost Pelvetia (i.e. slightly above the mean high-tide level), and is thus 

 only Hooded during spring-tides. It is characteristic of peaty shores. Where 

 the shore slopes, the Fucus vegetation forms a distinct narrow band ; but 

 where it is flat and salt-marsh conditions obtain, it is much more extensive, 

 and may pervade a large area of the marsh. As a band, it is widely 

 distributed in our area, being frequent in Achill Sound and Bellacragher Bay. 

 On the salt-marsh it is usually found on the best-drained areas. 



The association forms a dense mossy turf in which Glyceria maritima is 

 usxially abundant, and scattered plants of Statice maritima, Glaux maritima, 

 and Salicomia maritima also occur. Occasionally, however, small patches of 

 pure Fucus may be noted. The " turf " is composed of fastigiately branched 

 plants which are densely crowded together, with more than half their total 

 length (2-3 inches) buried in the peat. The growth is very erect ; but the 

 upright shoots are often found to arise from a more or less creeping stem. 



