76 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



Sweden was covered by this ice-cap, but as regards Norway, 

 the conditions are still a matter of dispute. Some geologists 

 maintain that the ice went right out into the sea on all sides ; 

 others assume that in some parts there was an iceless coast- 

 region, where only here and there great glaciers ran out into 

 the sea. 



The great majority of the species in the Norwegian flora 

 must, however, have immigrated after the last Glacial Period ; 

 but with regard to their immigration and the conditions under 

 which it took place, various theories have been advanced. 



The first to take up this question, especially with regard 

 to Sweden, was F. W. Areschoug {'66), who, in 1866, main- 

 tained that the present vegetation of Scandinavia was made 

 up of at least three elements of different period and origin, 

 namely : 



(1) An arctic vegetation, which immigrated from the east 

 during the latter part of the Glacial Period, and, from its 

 origin, may be called the North Siberian Flora; 



2) A northeastern and eastern vegetation, which came 

 into Europe from Siberia after the Glacial Period, but before 

 the immigration of the beech. From its origin, it may be 

 called the Altai Flora; 



(3) A southeastern and southern vegetation, which came 

 simultaneously with the beech, partly from the Caucasus and 

 the countries 'round the Caspian and Black Seas, partly from 

 the countries of the Mediterranean. This may be called the 

 Caucasian and Mediterranean Flora. 



Areschoug also pointed out that a number of arctic species 

 in the north German and south Swedish lowlands must be 

 regarded as relics of the vegetation of the high north, which, 

 after the melting of the ice-cap, withdrew toward the north 

 or up into the mountains. 



This view received strong support in the discovery by A. G. 

 Nathorst (71) in 1870, in the fresh- water clays of the south 

 of Sweden, of remains of typical arctic plants which do not 

 grow there now, but only very much farther north, namely, 

 Betula nana, Dryas octopetala, Salix herbacea, S. polaris, 



and S. reticulata. 



