806 



algal flora of the North Atlantic have originated from a mixture of 

 Atlantic and Arctic species. I shall briefly explain the main rea- 

 sons for this conclusion. 



There is hardly any doubt, that in tertiary times there has been 

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

 and Iceland to America. This explains the great resemblance that 

 exists nowadays between the algal florae on both sides of the ocean. 

 The flora north of the land-conneclion dilTered much from that which 

 grew^ south of it. The Arctic flora has gradually developed from that 

 north of the land-connection, and as pointed out by Kjellman, it is 

 an old flora, w^hich has developed in the seas about the Pole and has 

 been very rich in endemic species. But when the land-connection 

 w^as broken, w hich probably happened in the later Tertiary period, a 

 comingling 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 tliat a flora of Arctic character probably oc- 

 curred as far dowai as the coasts of South England and North 

 France. On its way south, however, this Arctic flora met and be- 

 came 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 composed of species from tw^o different territories, again 

 wandered towards the North, yet a few^ Arctic forms, which were able 

 to adapt themselves to the higher temperature, remained on the 

 coasts of England and France, w^hilst others withdrew^ to the Polar Sea 

 proper. On the other hand, several more southerly Atlantic forms 

 likewise followed northw^ards, and in such quantities, that they still 

 occur so numerously as to stamp the character of the algal flora 

 in places w^here circumstances were favourable to their grow^th, for 

 instance, on the northern coast of Norway. In some such manner 

 as this w^e may suppose, that the algal flora of the northern part 

 of the Atlantic Ocean has originated. At the end of the Glacial 

 Period its general appearance must have been much the same as it 

 is to-day: a comingling of old Atlantic and Arctic elements. 



The flora of the Faeroes and w^ith it the oceanic algal flora 

 were probably completely destroyed during the Glacial Period. How 

 have the Islands again recovered their flora, and in what manner 

 especially has the immigration of the marine algae taken place? 



