38 THE :m:atitn"i: alg.e or gueexset 



In contlitions of extreme exposure, F. veslculosus disappears 

 altogether; it is superseded by the var. evesiculostis, a characteristic 

 plant on exposed shores, which forms the continuation of the band of 

 JF. vesiculosus along such districts at about half tide. The fronds 

 are short, stout, about 4 inches long, very dark, with strong basal 

 disks and branches of equal length, as if cut with a knife. The plants 

 often protrude from patches of Licliina pygmcea^ or from holes and 

 chinks of the rock, wherever a little shelter is to be found for the 

 sporelings to start growth. Poh/siphonia fasticjiata is a frequent 

 epiphyte. 



Ascoplii/llum nodosum extends in varying profusion from Pezerie 

 Point to Grandes Rocques, where the climate is semi-exposed. A vast 

 expanse round Lihou and the adjacent islets measures many square 

 yards. As indicated by Cotton this plant largely depends upon 

 suitabilit}^ of substratum, for it can only grow on rocks of a height 

 that enables the fronds to hang down ; where rocks are flat or give 

 place to sand, it disappears. 



The relative positions of Ascopliyllum ?7odosum and Fucits 

 vesiculosus on the shore are interchangeable along the Guernsey 

 shores ; sometimes the one, sometimes the other, takes the higher 

 range and succeeds F. sjnralis. The determining factors, as already 

 pointed out, are very possibly the size and height of the rocks at the 

 respective levels ; the two alg;e frequently intermingle. 



The hummocks and rocks round Lihou seem specially favourable 

 for the growth of Ascopliyllum. Its luxuriance there is also pro- 

 bably due in great measure to the prevalence of surf; where the 

 extreme roughness of the coast creating this condition ceases, as 

 beyond Grandes Rocques, it no longer figures as a conspicuous feature 

 of the shore. Further along the band becomes much broken. 

 Patches of varying size can be seen in moderately sheltered localities 

 in the north at L'Ancresse Bay, and in the east at St, Peter's Port ; 

 but in extreme shelter only a few plants are to be found scattered 

 here and there among F. vesiculosus, e.g. Petit Bot. 



F. serratus occurs along the lower portion of the littoral and is 

 always found covering low^ llat rocks ; hence where these do not exist, 

 a break in the continuity of the band results. The growth is ver^^ 

 restricted and does not form a well-marked zone : it is favoured by 

 shelter, but exposure is inimical. Often, where there is partial 

 exposure, F. vesiculosus takes its place and extends in that case down 

 to lovv-w^ater mark ; except as a pool-plant F. serratus is absent 

 wdiere conditions of extreme exposure prevail. Bpermotliamnion 

 Turneri and Elacliistea fucicola are frequent epiphytes. 



The follow^ing species form undergrowths of both F. serrains and 

 Ascopliyllum nodosum: — Cladopliora rupesfris, Hildenhrandtia sp., 

 Lithotliamnion Lenormandi, Gelidium crinale, Enferomorplia coni- 

 pressciy etc. 



Li china Zone. 



Licliina conjinis grows over rocks here and there, and was specially 

 noted at Rocquaine Bay below the Hotel Imperial. Miss Knowles 



