Clare Island Survey — Marine Algae. 15 29 



found on flat rocks, and rarely on the perpendicular faces. The rock-surface 

 may be rugged or smooth, and a very favourite substratum is that of mussels. 

 In all cases the rocks are exposed ; and often the most vigorous patches are 

 those where the waves strike with great force. The normal position of 

 Porphyra is in the upper part of the littoral region, where it occurs as a band 

 a short distance below Pelvetia. In some cases the band is quite narrow, as 

 is shown in Plate I, where it occurs between Pelvetia and F. vesiculosus, taking 

 the place of Fucks spiralis ; in others it is mixed with F. spiralis, and runs 

 down through the wider belt of F. vesiculosus that follows. Porphyra also 

 occurs where the Fucaceae are absent, and is here commonly mingled with 

 Bangia or Ceramium acanthonotum. At Kinnacorra it is found on smooth 

 sloping rocks devoid of vegetation, and forms a fairly wide band from a short 

 distance below high-water mark down to about half-tide, at which level 

 Bangia takes its place. In this position, being quite unprotected from the 

 sun, it becomes very dry and disappears during summer. 



A very distinct aspect is acquired by the association during winter, owiug 

 to the presence of an abundant growth of var. linearis. This plant, though 

 often regarded as a distinct species, represents sporelings of P. umbilicalis, 

 which at that season are elongated and tapering. The growth appears first in 

 October, and develops rapidly during the winter, frequently covering boulders 

 and smooth rocks over extensive areas. It is usually quite distinct from the 

 normal Porphyra association, and forms a band above it. In March the 

 effect of drying winds and increased sunlight is felt, and much of the growth 

 dies. By April var. linearis has disappeared, except in lower and shaded 

 places. 



With regard to the supra-littoral growth, the contrast between Clare 

 Island and the Faeroes is most marked. In a few spots Porphyra was noted as 

 extending into the Pelvetia band on Clare Island ; and at Alnahaskilla it was 

 found at the highest tide-level on the north side of steep bare rocks, a sample 

 of the kind of growth that takes place on a much larger scale on the Faeroes. 

 Below the big cliff on the north side of the island, where the shore is steep 

 and the rocks fully open to the Atlantic, Porphyra was one of the few algae 

 that were noted in the littoral zone. But even here, with shade and continual 

 spray, there was no supra-littoral growth comparable to that described by 

 Borgesen. Its growth probably exceeded the limit of high- water level (which, 

 owing to the constant swell, is not easy to determine), but not to any remark- 

 able extent. In the Faeroes, on the other hand, even in sheltered localities, 

 the lowest limit is at high- water mark, and in exposed situations it is not 

 found till far above that level. 



Kjellmann and other Scandinavian algologists have regarded the Porphyra 



