

[Vol. 2 



96 ANNALS OK THE MISSOURI BOTANICAL GARDEN 



Tapes Period, i.e., the Scandinavian Paleolithic Age. On 

 the other hand, R. Sernander believes that at the beginning 

 of the Iron Age — about 2,400 years before our own day — so 

 great a decline in temperature ensued that the montane plants 

 made their way into the lowlands in many places. He inter- 

 prets the present occurrences of alpine plants in the lowlands 

 as relics from that period. This can, however, be the case 

 only to a certain extent, for there is no doubt that at the 

 present day alpine plants spread down to the lowlands and 

 continue to grow there, provided the conditions are favorable. 

 R. Sernander gives to his assumed cold, damp period at the 

 beginning of the Iron Age the name employed by A. Blytt, 

 the " sub- Atlantic period"; but the two have, in reality, very 

 little to do with one another. A. Blytt states that his sub- 

 Atlantic period occurred when the south coast of Norway 

 lay from 30 to 50 feet lower than its present level, which 

 would answer to the beerinninij: of the Bronze Ag;e. He men- 



6""""0 "■"- ""^ -l^iWXX^V, x-^ 



tions, among other species that immigrated during the sub- 

 Atlantic period, Carex Pseudocyperus and Cladium Mariscus, 

 which had already immigrated in the Pine Period, and Cera- 

 tophyllum demersum, which had immigrated in the Oak 

 Period, besides two or three species that were certainly im- 

 ported later in foreign grain and grass seed. 



I do not yet consider R. Sernander 's cold, damp "sub- 

 Atlantic period" at the beginning of the Iron Age to have 

 been clearly proved, although there are a few facts that speak 

 in its favor. But even if such a cold, damp period did super- 

 vene, its principal effect would have been to decimate the oak 

 flora — in localities that were not especially warm — more 

 rapidly than if the climate had gradually become colder from 

 the Stone Age to the present time, as most people believe. 

 Similarly, it may have promoted the occasional descent of 

 montane plants to the lowlands, but it appears that this can 

 also take place under the present climatic conditions, without 

 the necessity of having recourse to relic occurrences from the 

 "sub- Atlantic" or even from the "Dryas Period." 



An instance of such an occurrence is that of Dryas octo- 

 petala at Langesund in southeastern Norway. This species 



