15 56 Proceedings of the Royal Irish Academy. 



and var. laterifructus not infrequent. In many localities var. axillaris is 

 found, which under certain conditions passes into F. volubilis, Huds. The 

 latter in its typical form was not noted in the area ; but the salt-marsh 

 plant var. baltica is abundant. This, together with a peculiar variety named 

 mmcoides. is dealt with later (p. 80). 



(d) Fueus serratus. Whilst Ascophyllum enjoys hanging from boulders, 

 F. serratus prefers to lie flat. Occasionally it is found growing on sand-covered 

 rocks, and then rests on the bare sand. It is found on all sheltered coasts 

 where there is appropriate anchorage ; but in many parts of Clew Bay this is 

 wanting; and the pebble-attached association sets in below F. vesi-culosus. 

 F. serratus forms a band which unites the littoral and sub-littoral regions. 

 The fronds are wider on sheltered than on exposed coasts ; and on the whole 

 it is the least variable Fucus. 



Sub-vegetation, — When growing on sloping rocks a luxuriant undergrowth 

 of various algae is found ; but when attached to stones, or where much sand 

 occurs, extraneous species are scarce. Amongst those almost constantly 

 present are : — 



In upper part. In lower part. 



Hildenbrandtia. Cladostephus spongiosis. 



Catenella. Ulva. 



Gelidium pusillum. Ceramium rubrum, 



Cladophora rupestris. Chondrus. 



Gigartina. 

 C. rupestris. 

 On the more open shores where clean rocks are prevalent, the Laurencia- 

 Gigartina vegetation often forms the main undergrowth, though upward 

 extensions of the Corallina-Lithothamnium association are also frequent. 

 Amongst these.sueh sub-littoral or shade-loving plants as Chylodadia articulata, 

 Delesseria alata, and Plumaria occur, with many odd plants of various 

 communities. In sandy places a Ilhodochorton floridulum vegetation is often 

 developed, and this ousts many of the other species. 



Epiphytes. — These are likewise fewer in very sheltered than in moderately 

 open localities. In the quiet reaches of Clew Bay, Pylaiella is always present 

 and forms in spring and summer large floating masses. Other frequent 

 epiphytes are : — . 



Dictyosiphon foemculaceus. Ectocarpus siliculosus. 



Ceramium rubrum. E. tomentosus. 



C. Boergesenii. E. fasciculatus. 



In late summer blue-green algae are much in evidence, Calothrix 

 confervicola and Rivularia atra occurring everywhere, often accompanied by 



