15 84 Proceedings of the Royal Irish Academy. 



mouths of rivers. Though certain species are found to be constant, it is 

 difficult to obtain generalizations as to the position and sequence of the plant- 

 societies ; and a detailed account is more apt to be merely descriptive of a 

 particular locality. Opportunities for comparison are fewer, not only owing 

 to the small number of streams available, but on account of the different 

 physical conditions afforded by each. In Clew Bay, for instance, there are 

 but three rivers, the floras of which are very different. The Newport river has 

 bants strewn with rocks and stones on which Fucus develops ; whilst the 

 banks of the Bunowen are loamy and possess a vegetation of Chlorophyceae 

 and Cyanophyceae. The Westport river is again different. There is also a 

 stream at Belclare which issues as a waterfall amongst rocks in the midst of a 

 luxuriant growth of Fucus ceranoides, and then disperses itself on a muddy 

 shore. In contrast to the above the hill-side streams that descend into 

 Bellacragher Bay and Achill Sound are fairly constant in their flora. 

 For the above reasons it is more satisfactory to treat the vegetation of each 

 stream as such, and not to attempt a general account. 



The Newport Paver. 



This river is tidal for about 3 miles, and has fairly wide banks which 

 support two well-marked plant-communities, namely, an Enteromorpha 

 association and a Fucaceae association of brackish type. The conditions with 

 regard to salinity in such a river are unusually complicated. During heavy 

 rains, the banks may be flooded with fresh water brought down by the stream 

 to a much higher level than usual, and the algae composing the vegetation 

 must be able to endure, not only regular change due to tide, but also 

 prolonged submersion in fresh water. 



(1) Enteromorpha Association. — This consists chiefly of E. intestinalis, 

 E. prolifera, and E. clathrata, together with the numerous intermediate forms 

 characteristic of brackish waters. The growth is most irregular and perplex- 

 ing, and, as the Ulva investigations had shown, any attempt to name all the 

 forms occuring is at present hopeless. Time, therefore, was not wasted on 

 the genus. 



(2) Fucaceae Association. — Fucus was more interesting, the most extensive 

 growth of F. ceranoides seen in the district occurring here. Starting from the 

 mouth of the river, there is a vegetation composed of Pelvetia, F. spiralis, 

 Ascophyllum, and F. vesicidosus. On walking towards Newport F. ceranoides 

 soon appears. This takes the place of F. spiralis, and lower part of the 

 Pelvetia belt. The latter, however, remains a little longer, especially on 

 boulders. F. ceranoides meanwhile increases, and gradually usurps the 



