[Vol. 2 



84 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



coast margin and there managed to survive that period, and 

 then to some extent followed the retreating ice up to the 

 mountains where thoy are now found. 



Andr. M. Hansen ( '04, '04 a ) even assumes that at least 300, 

 perhaps as many as 500, kinds of vascular plants may have 

 lived upon this supposed iceless strip of coast, which he as- 

 sumes to have been fairly broad. These figures are perhaps 

 rather high, but it is not j)ossible to make more exact state- 

 ments until paleobotanical investigations have been carried 

 out in the peat-bogs in these regions. 



Against the second possibility, namely, that the arctic 

 plants may not have immigrated from Denmark to Kristians- 

 sand until after the ice had withdrawn, several facts may be 



cited. 



These arctic plants, farther up the west coast of Norway 

 (e.g., in Nordfjord), are found together with Yoldia arctica, 

 and thus in a decidedly arctic climate, while those near Kristi- 

 anssand, though, indeed, found with Yoldia, also occur with 

 Mytilus, which indicates that the climate was somewhat 

 milder and that the plants originated at a more recent period 

 than those in Nordfjord. Thus the arctic plants, e.g., those 

 in Nordfjord, cannot have immigrated thither from Kristians- 

 sand, but may be assumed to have been there during the Last 

 Glacial Period. 



On the other hand, Salix polaris near Kristiania, which ap- 

 pears to have originated at a somewhat later period, may 

 have been able to immigrate thither along the margin of the 

 ice from Kristianssand ; but this cannot at present be stated 

 with certainty, as no fossils have been found between the two 

 points. 



THE BETULA ODORATA PERIOD 



As the ice-cap withdrew and the climate became milder, 

 the land began to rise. In the center and south of Sweden, 

 this took place so rapidly that a land connection was formed 

 between Sweden and Denmark, and also between south and 

 north Sweden, very much as it is at present. The Baltic 

 thereby became a lake, its waters becoming gradually fresher 

 and containing fresh-water animals, especially Ancylus fluvia- 



