THE MARINE Al.G.T, OP (iUERNSEV 33 



I, The Exposed Type, 



This type is well represented at Pleininont, where the sliore is 

 rugged with a moderate slope, and the general appearance is desolate 

 and bare. According to Rattray this bareness oi: rocks in an exposed 

 j/iosition is " owing to the force of waves from deep water, wheie})y 

 rhizoids or thalli are removed from the substratum, and the matura- 

 tion of fruit is prevented. In sucli places there are fewer })lants and 

 of stunted growth." In view of this it is interesting to note in the 

 chinks and fissures the occasional presence of certain matted species — 

 e. g. Poli/siiihoJiia macrocarpa, Gle)iosipJionia liijpnoidcs — which hold 

 sand, shells, etc., iu their interstices and serve as a nidus for spores 

 of other species, patches of Lichina pijtjmcda on the rocks and 

 boulders also form whole nurseries for sporelings of Fuciis, etc. Lami- 

 naria digitata occurs profusely, whilst beyond the limit of low 

 tide, the erect snaky stipes of L, Gloustoni are seen standing up out 

 of the water. There is very little Pel vet la or F. sjjiralis. 



It w^as not possible to observe the extent of these growths owing 

 to the difficulty of obtaining a boat. The inky patches of lichens, 

 the dark tufts of Fuciis vcsiculosus var. evesicidosus along the mid- 

 littoral, and the dull pads of CyanopliiicecB along the upper littoral, 

 produce a sombre effect. Deep clefts and masses of rock afford con- 

 siderable shelter, which brings about minor modifications of the 

 general type. 



II. The Semi-exposed Type. 



The west ahd north-west coast of Guernsey, with its five bays, is 

 distinctly exposed to the north-westerly winds and the force of 

 Channel waves ; the bays ai-e cut by reefs running at right angles to 

 the shore, and they are further sheltered by a fringe of islets and sharp 

 rocks which form a barrier shutting them in from the open sea ; these 

 sheltering rocks profoundly modify the stormy nature of such a coast 

 and give rise to conditions of semi-exposure. 



Though not dominant, Pelvetia appears here and there in the 

 upper areas in scattered tufts, increasing occasionally into large 

 patches. Fncus spiralis also is well marked, but gives place lower 

 down "to Ascophyllum nodosum. The latter, according to Cotton, 

 grows only in conditions of considerable shelter, but the opposite was 

 found to be the case in Guernsey, where it prefers the semi-exposed 

 and modemtely sheltered habitats. It evidently thrives in the surf 

 set up by the rock^^ conditions, and an enormous tract of this alga 

 forms the great feature of the Semi-Exposed coast. F. serrahis is 

 infrequent, and is replaced in many instances by F. vesiculosns. 

 Himanthalia is also scarce. Stretches of sand in this area form 

 habitats for Polysiphonia nigrescens, Ahnfeltin plicata^ Clados- 

 tephus verticiU edits, Oracilaria confei'voides, and Chondria tenuis- 

 sima. Zostera beds with intervening groups of rock occur at low- 

 water mark. Another dominant note is Bhodymenia palmata : 

 heavy growths hang from rocks and boulders along the lower littoral, 

 and take the place of Ascophyllum nodosum where there is less surf ; 

 for instance, along Portelet, llocquaine Bay, etc. The LaminaricB 



JOUKNAL OF BOTANV, AuiiUST, 1920. [SUPPLEMENT II. 1 d 



