THE MAKINE ALG.E OF GUEIINSKV 45 



from thence into the North Atlantic. The Arctic Algte occurring in 

 Guernsey are given below ; the}^ are also common to the English and 

 French coasts, and three of them, marked with an asterisk, are 

 cosmopolitan : — 



Rlioclochorton Rothii. Chceiopteris plumosa. 



Fucus vesiculosus* Ectocarpns confervoides. 



F. ceranoides. I^ylaiella littoralis* 



Chorda Jihim. Enteromorpha compressa. 



Malfsia detiRta. Rhizocloniiim riparium. 



Elacliisfea fucicola. Urospoj-a penicilliformis. 



Scytosiplion lomentarius* LitJiotliamnion polymorplium. 



Desmarestia viridis. Rhodymenia palmata. 



D. aculeata. Ahnfeltia plicata. 



Dicfyosiphoiifoeniculaceus. Ceramium ruhricm. 



The origin of this Arctic element is graphically described by 

 Borgesen, from whom the following is taken : — " The European- 

 American algal Flora of the North Atlantic has originated from a 

 mixture of Atlantic and Arctic species. In tertiary times there was 

 a land-connection reaching from Europe by means of the Faeroes and 

 Iceland to America The Arctic Flora has gradually de- 

 veloped north of the land-connection ; it is an old Flora, which has 

 developed in the seas about the Pole, and has been very rich in 

 endemic species. But when the land-connection was broken up, 

 probably in the later tertiary period, a commingling of the species 

 from the two formerly separated territories began and continued into 

 the Glacial Period. During the latter, when the Polar Sea and the 

 northern part of the Atlantic Ocean were covered by great masses of 

 ice, the algal Flora was forced to go southwards, so that a Flora of 

 Arctic character probably occurred as far down as the coasts of South 

 England and North France. On its way south, however, this Arctic 

 Flora met and became intermingled with the species of the Atlantic 

 Flora, which had been able to resist the climatic changes. When the 

 ice again receded after the Glacial Period, this algal flora, now com- 

 posed of species from two different territories, again wandered towards 

 the north, yet a few Arctic forms which were able to adapt themselves 

 to a higher temperature remained on the coasts of England and 

 France, while others withdrew to the Polar Sea proj^er." 



SOUTUERN ElEMEXT. 



The southern element of the Guernsey Flora includes a very large 

 number of Mediterranean sj)ecies ; some are even natives of the 

 Indian Ocean, Brazil, West Indies, etc. There is a continual immi- 

 gration northward of these southern species ; man\^ have long 

 established habitats in the warmer parts of the Atlantic Ocean, 

 whence they have travelled to the shores of Northern France, 

 Guernsey, South of England, and even Scotland. The Floridece 

 dominate the southern type of Flora, though the Phceophycece and 



