15 88 Proceedings of the Royal Irish Academy. 



The Monostroma vegetation is at its best in spring (April and May). It 

 then occurs in deltoid patches, reaching from above F. ceraiioides to- about 

 half-tide level. It covers the rocks and stones in the stream with a dense 

 covering : and also spreads out on either side, growing chiefly on the Fucus. 

 The plants in the streams remain submerged ; but those outside are exposed 

 at low-water, and in fine weather dry up rapidly, appearing as a brittle skin, 

 which crackles in the hand. As summer advances, the flank-growth 

 disappears ; but in the streams themselves Monostroma was found in plenty 

 during each visit. 



v. VegetoMon of Brackish Bays. 



The vegetation of inlets surrounded by mountains from which streams 

 descend possesses several distinctive features, and must be recognized as afford- 

 ing a definite vegetation-type. Certain species of diatoms are abundant, also 

 Cyanophyceae ; whilst the complete absence of several of the larger algae, and 

 the prevalence of others, are also noticeable. 



Other factors, besides the addition of fresh water, have, however, to be 

 considered. Being more or less land-locked, the tide is slight, and the condi- 

 tions exceedingly tranquil : consequently the aeration of the water is probably 

 very poor. Mineral salts moreover are brought down by the streams, and in 

 our area peaty acids and other compounds from the peat-bogs are doubtless 

 plentiful, the streams being deep brown in times of much rain. 



Bellacragher Bay was selected as a spot for systematic investigation. It 

 is land-locked, and, except for a few months in summer, receives a large 

 amount of fresh water. Samples of water taken in August showed almost 

 normal salinity, but this was after the dry summer of 1911. This inlet is, 

 therefore, not an extreme case; but the features shown may be useful for this 

 very reason. Bays of much feebler salinity doubtless occur in Ireland, as 

 they do abundantly in the west of Scotland. 



The following associations are represented in Bellacragher Bay : — 

 Hildeiibraiuhid-Yrrrvxario. — Very well marked on stones and pebbles 

 from half-tide downwards, ascending higher in damp places. 

 eae. — All five species present. Fronds of F. serratus narrow. F. cera,- 

 twides forming delta-like patches at the bottoms of streams, but not 

 general in any part of the bay. 

 Lichina. — Very feebly developed. L. confinis most frequent. 

 Lanraicia-Gigartijui. — Poor. Isolated patches in sub-littoral region 



common. 

 Lamina ria. — Sub-association of L. saccharina on big stones and blocks of 

 rock frequent. Plants usually long, but not wide, 10 to 12 ft. by 1 ft. 



