1915] 



WILLE FLORA OP NORWAY 93 



southwestern lowlands, that it can hardly be imagined that 

 it migrated along the coast to the west and Trondhjem. 



It must therefore be taken for granted that these plants 

 migrated by way of the mountain passes, some of which now 

 lie at such an altitude that even Pinus sylvestris cannot live 

 in the highest localities. But I have already mentioned that 

 the summer temperature during this period was about 2.5° C. 

 higher than it now is. We see, moreover, that remains of 

 pine forests are found on the mountains in Norway, e.g., on 

 the Dovre Mountains in central Norway, and on the Hard- 

 anger plateau in the south of Norway, respectively 990 and 

 1,470 feet above the present highest limit of Pinus sylvestris. 

 Under the then existing climatic conditions, the now treeless 

 passes were clothed with forest, and warmth-loving plants 

 were able to spread through them. 



A. Blytt, and after him R. Sernander, distinguishes between 

 a boreal and a sub-boreal flora, the members of which are 

 supposed to have been lovers of warmth and dryness, but 

 separated in their immigration by an Atlantic flora that loved 

 humidity and warmth. With this I cannot agree. Several of 

 the species that Blytt ('82) classes under "sub-boreal" are 

 found in a fossilized state together with those he calls "bor- 

 eal"; and around Kristiania many species of these so-called 

 different floras grow together under exactly the same condi- 

 tions in the same localities. 



It seems likely, however, that the climate was more humid 

 during the Littorina Subsidence, when the water of the Gulf 

 Stream could make its way directly into the Baltic across 

 central Sweden. A. Blytt ('82, p. 23) says: "Man darf des- 

 halb mit einem hohen Grad von Wahrscheinlichkeit be- 

 haupten, dass die atlantische Flora in dieser Regenzeit einge- 

 wandert ist, und ihren Weg rund um den Christianiafjord 

 gefunden hat (in derselben Weise, wie unter der folgenden 

 Regenzeit die subatlantische)." I cannot agree in all respects 

 with this. Those forms which Blytt calls "atlantische Arten" 

 include a great number of species, of which some occur in 

 what I have here called the "region of Hex Aquifolium," 

 others constitute what I have called the "west European 



