Glare Island Survey — Marine Algae. 15 17 



The distinction between associations and societies is more puzzling- 

 Many of the small communities that have been described by various writers 

 appear to represent societies (as understood by Tansley and Moss) rather 

 than associations ; caution, however, is needed, as definite zonation is 

 discernible in one locality, whilst in others the growth is patchy and discon- 

 tinuous. For this reason I have adopted a conservative attitude in the 

 present report, and have used the term ' association ' instead of replacing it 

 by that of ' society.' In the ease of communities described for the first 

 time, when the status was doubtful, a non-committal expression has been 

 used. The whole question of transient societies requires careful working 

 out. Many algae appear periodically, and of these some are short-lived, 

 being conspicuous only for a few weeks, whilst others require six or eight 

 months to complete their life-cycle. It is clear, therefore, that before the 

 status of these communities can be settled, a more complete knowledge of 

 the seasonable range of many species is needed, as well as a more detailed 

 analysis of the vegetation. 



3.— The Vegetation of the Area. 

 i — The Rocky-shore Formation. 



The rocky-shore formation embraces every form of hard ground, from the 

 exposed rugged slates of Clare Island, to the flat low-lying sandstones of 

 Clew Bay. Great variety in slope and exposure is met with, and also in the 

 surface and hardness of the rock. Speaking generally, the formation is 

 characteristic of open shores. In exposed localities it is the only one to be 

 found. On sheltered shores it is not infrequently poorly developed, or 

 replaced by the sand-and-rock or sandy-mud series. A characteristic feature 

 is the strong basal disk by which the plants are attached, this being true 

 both of exposed and sheltered coasts. Some of the smaller species have, 

 however, other methods of attachment, as explained later. The vegetation of 

 boulder-beaches is included in the formation, and also that of more or less 

 buried rocks and stones, though, in the latter case, the vegetation clearly 

 approaches that of sand-and-rock (pp. 65-67). The pebble-attached association 

 of quiet bays, being characteristic of a soft bottom and not of rock, is placed 

 ■pro tern, under the sand-formation. 



The associations differ markedly according to the amount of exposure, and 

 two series are to be recognized — namely, exposed and sheltered. The littoral 

 and sub-littoral vegetation must also be distinguished ; but, except for these, 

 no further sub-division has been attempted. The hardness of the rock, and 



Ji.I.A. PROC, VOL. XXXI- C 15 



