26 THE MAIilXE ALG^ OF GUEBNSEY 



Cr. C. ET.OXGATA Johiist. {C. meiliierrcinea Aresch.). W. 1. E. 6. 



C. SQTJAMATA ElHs. C. E. 9. 

 CM. C. AIBUATA Zaii. S.W. v.r. 



C. EFBENS Ellis and Solan. {Jania ruhnis Lam. ). f.c— var, 



cornicidata Haiick. (J. corniculata Lam.). [N.W. 4. S. o. 



W. 4.] S.W. r. 



TIL Some Ecological Factors. 



The methods of plant ecology have of recent years been applied 

 to marine botany, and many new facts have been ascertained con- 

 cerning the growth and distribution of Alga?. These subjects need 

 still further investigation, though Harvey, Rattray, Murray, Darby- 

 shire, etc., have furnished valuable contributions towards the know- 

 ledge of the subject. 



One of the most recent workers in marine ecology is Mr. A. D. 

 Cotton. His Report on the excessive growth of Ulva latissima in 

 Belfast Lough (1911) and that on the Marine Algse of Clare Island 

 (1912) are standard works. The former deals very fully with the 

 various conditions determining the presence etc. of Alga?, and clearly 

 demonstrates the connection between a mud-formation and an Ulva- 

 association. In the latter, Mr. Cotton has established the subject of 

 marine ecology of Britain on a definite basis by subdividing the 

 Alga? of a given district^that of Clare Island and the neighbouring 

 shores — with regard to their habitat, degree of exposure, shelter, etc., 

 into certain '• formations " or types of vegetation and their con- 

 comitant " associations." For though foreign algologists, such as 

 Kjelmann, Borgesen, Jonsson, and various others have dealt very 

 fully with the subject of marine ecology, Mr. Cotton's are the first 

 organised and comprehensive works of the kind produced in England. 

 They therefore serve as a useful guide in subsequent studies of 

 marine algal distribution in Britain. 



(1) JPhysical Position of the Island. 



The tidal stream flows up the English Channel in the direction 

 E. by N., and falls "W. by S.W. Guernsey is so situated that it 

 stands right out in the southern portion of the stream and interrupts 

 the normal flow of the body of water. Striking against the Channel 

 Islands, the stream divides'^and flows on either side of them and also 

 eddies round the Gulf of St. Malo. Spores, fragments, or plants of 

 algoid nature carried as flotsam would stand a good chance of being 

 intercepted by the obstructing rocks and islands, so that the prolific 

 marine vegetation of the Channel Islands, including the presence of 

 fspecies not found on the British coasts, is largely owing to its geo- 

 graphical position. 



(2) Tides. 



Mean spring tides rise about 26 ft., with a corresponding fall. An 

 enormous expanse of most varied character is exposed by the ebbing 

 tide, thus a:ffording a wide area for collecting ; but the rapid rise 

 and fall renders the ground somewhat dangerous — the collector, 

 unless familiar with the shore, is apt to be cut off. 



