15 34 Proceedings of the Royal Irish Academy. 



naturally regarded as forming a single belt. In a general way Laurencia 

 prefers a certain amount of shelter, and thrives on sloping or flat rocks, whereas 

 Gigartina enjoys the roughest water and steep surfaces. On comparing this 

 plant-community with those of other countries, it was found that the joint 

 belts formed by the two species in Clare Island corresponded to Borgesen's 

 Gigartina association in the Faeroes — a conclusion which was confirmed by 

 him during his visit. It was thought best, therefore, to connect the Irish type 

 of vegetation with the Faeroese, and the name Laurencia-Gigartina association 

 has been given. In the Faeroes Laurencia is very rare, being found oidy in 

 pools. 



The Gigartina band may be dealt with first. On exposed coasts it is 

 barely uncovered during neap-tides, but with spring-tides a distinct belt 

 reaching down to the Alaria and L. digitata zone is revealed. It is frequently 

 accompanied by a certain amount of the narrow form of Ghondrus crisyms. 

 Well seen on vertical rocks, where it forms a band 2 feet deep, it also occurs 

 on flat and sloping surfaces, here usually as an undergrowth to Himanthalia. 

 On the open coasts it is often accompanied by the following algae, all of 

 which are known to enjoy the turbulent conditions of low-water mark: — 



Scytosiphon lomentarius. Plocamium coceineum. 



Rhizoclonium implexum. Polysiphonia thuyoides. 



Chylocladia ovalis. P. Brodiaei. 



Lomentaria clavellosa. Corallina squarnata. 



The Gigartina belt occurs also on the more sheltered ground at Portlea. 

 It first appears well up in the Laurencia band ; but as the lower levels 

 of the littoral region are reached, it increases greatly in quantity, till finally 

 it occurs as a pure growth covering comparatively large areas. At Kinnacorra, 

 on the other hand, where there are varying degrees of exposure, the Gigartina 

 vegetation is practically absent. 



Passing now to Laurencia, we find this is more conspicuous on account of 

 its truly littoral habit. It begins shortly below the half-tide level, and runs 

 down into the Himanthalia association. It is common on moderately exposed 

 shores, and appears to prefer clean, gently sloping rocks where sand is absent. 

 Under these conditions Laurencia may exist as a pure growth 2 or 3 yards 

 wide, but where the shore is flat it extends over a much wider area, being 

 then mixed with other species. When sand is present it gradually gives place 

 to Rhodochorton florididum. 



In its lower levels the Laurencia belt forms an undergrowth to Himan- 

 thalia, and on sheltered shores occurs in a similar manner beneath F. serratus. 

 It is found at times under F. vesiculosus, and thus runs upwards considerably 



