32 THE MAHrXE ALG.E OF GUERNSEY 



(b) Types in relation to Habitat and Climate. 



The coast of Guernsey being mainly of a rocky nature, the marine 

 vegetation is for the most part sa.vicoloics, and the plants are either 

 characterized by strong basal disks and attachments — e.g. Fucusspp., 

 Laminaria spp., etc. — or form incrustations, such as Ralfsia, Litho- 

 thamnion, etc. 



Here and there Avhere disintegration of the rocks is complete, 

 resulting in patches of sand along bays etc., the Flora is of a 

 psamniophilous nature. It includes various Cyanophycew whose 

 gelatinous sheaths hold particles of sand together ; '' their threads 

 permeate the sand to a depth of three millimetres" (Warming), 

 Catenella repens, Rhodochorton Jioridulum., Poli/siphonia niyrescens^ 

 P. obscura, etc., are also sand-dwellers ; they hold the sand by means 

 of filamentous rhizoids, thus forming tufts or pads which extend into 

 compact masses. When disintegration is partial, exhibiting the 

 intermediate stages of low rocks and pebbles, the character of the 

 vegetation is transitional, pertaining partly to sand and partly to 

 rock-floras, though possessing also distinctive characteristics. The 

 plants are usually short, bushy, and much divided. The vegetation 

 of shallow pools and channels also belongs to this category, which 

 includes Gladostephus, Mesogloia, Chondrus crispi/s, etc. (Cotton). 



Extreme conditions of disintegration have produced muddy 

 patches often thickly beset with Zostera, This marine phanerogam 

 by its horizontal roots acts as a capturer of the mud (Warming) ; 

 upon its stems an abundant epiphytic growth occurs, including 

 Ceraniium spp., Castagnea Zosterce, etc ; these, together with such 

 plants as Laminaria saccharina, Chorda filum. Sti/pocaulon, Ecto- 

 carpns granulosus, constitute the vegetation of Zostera beds. The 

 series merge constantly into each other, following the varied nature 

 of the coast-line. 



Certain modifications in a Flora produced by differences in aspect, 

 as described by Cotton, are clearl}^ seen in Guernsey, where four dis- 

 tinct types of vegetation coincide in each case with certain climatic 

 conditions. The dominant species are as follows : — 



Type I. The exposed, on the S.W. coast : 



Fucus vesical osus var. evesiculosiis, Licit ina pygmcea^ 

 Laminaria digitata, Corallina, LitJiothamnion. 



Type II. The semi-exposed, on the W. and N.W. coasts : 



Ascophyllum nodosum, Bhodymenia palmata, La- 

 minaria Gloustoni. 



Type III. The sheltered, on the S. and S. E. coasts : 



Porjyhyra, Enieromorpha intestinalis, Fucus vesicu- 

 losus, RJiody menia pal niata, LAiminaria saccharina. 



Type IV. The moderately sheltered, on the N. and E. coasts : 



Transitional llora with much intermingling of 

 zones. — Fucus scrt-atus, Rhudy)uenia palmata, ILi- 

 manthalia, Bifurcaria tuberculata, Laminaria digi- 

 tata. 



