16 VEGETATION IN COLOKADO-HOLM. [Mmioibs nat,osal 



[Vol. XIX, 



Chapter 3. 

 THE HISTORY OF THE ALPINE FLORA. 



We have seen from the enumeration of the species and the subsequent tabulation of those 

 which are common to both worlds that the Alpine vegetation is composed of members of the 

 present Arctic flora, of members of the mountainous flora throughout the Northern Hemi- 

 sphere, and finally of types peculiar to North America. In other words, some of these plants 

 exhibit a geographical distribution of enormous range. It is altogether a commingling of 

 types having originated from centers very remote and comprising not a few members of the 

 circumpolar flora. Nevertheless when we consider the data given with reference to the corre- 

 sponding vegetation, the Alpine, of the European Mountains, we obtain exactly the same 

 result, the composition of types being principally the same: Alpine, endemic, Arctic, and 

 circumpolar. 



The Arctic, and especially the circumpolar element, naturally points toward the conclusion 

 that these plants formerly belonged to the Arctic flora, but having been driven south during 

 the glacial epoch they sought refuge on these mountains. In Europe the important discovery 

 of fossil glacial plants proved the correctness of this supposition, and Nathorst * has offered 

 an excellent explanation of this problem. This naturalist succeeded in detecting a number of 

 leaves of Arctic plants hi glacial deposits in southern Sweden and Germany, among which were 

 Salix polaris, S. herbacea, S. reticulata, Dryas octopetala, Betula nana, etc. In the lowlands of 

 Zurich, Switzerland, Nathorst made the same discovery, and it is a most important fact that 

 Salix polaris should occur there in a fossil state, since it is a native of the most northern regions. 

 Some of the other plants — for instance, Dryas octopetala, Polygonum viviparum, Azalea pro- 

 cumbens, etc. — are now inhabitants of the Alps as well as of the Arctic regions. Thus the low- 

 lands of middle Europe did harbor an Arctic vegetation during the glacial epoch which after- 

 wards returned to the north when the ice receded, and most probably accompanied by Alpine 

 species, natives of the European Alps. Some Arctic species were, however, able to persist in 

 these mountains, notably Dryas, Azalea, Polygonum, etc. Thus they are in recent time 

 inhabitants of both the Arctic and Alpine regions, while Salix polaris, unable to endure even 

 the Alpine climate, returned to the polar regions. 



In the Carpathian Mountains several Siberian species are known to occur, some of which 

 are common to the Alps, some others not. Even the Caucasus is, in spite of the southern lat- 

 itude, remarkably rich in glacial species, and it seems natural to suppose that if they were able 

 to reach these mountains the Alpine flora might, at least partly, have been able to migrate north, 

 thus entering the Arctic regions. The recent Arctic flora may thus contain species contributed 

 from the southern mountains intermingled with those that originated in the polar regions. 

 With regard to Asia, Nathorst calls attention to the enormous distribution of the flora of Altai 

 due to the absence of inland ice. Thus the species were not prevented from migration to the 

 north or south in accordance with climatologic conditions. As a matter of fact, members of 

 the Altai flora are now to be found not only in the Arctic regions, but also in the Himalayas, 

 and several found their way to Arctic America and Greenland, where they are still in existence. 

 With respect to North America, the Rocky Mountains have no doubt contributed to the Arctic 

 flora, inasmuch as they are harboring a number of glacial species. 



The power of certain Arctic species to adapt themselves so as to thrive and persist on the 

 higher mountains farther south, as well as the Alpine species being capable of migrating north 

 together with the Arctic and to locate there, are the factors that govern the remarkable 

 distribution of Alpine, Arctic, and circumpolar species; and most remarkable is the fact that 



1 Polarforskningens Bidrag till Forntidens Vaextgeografl (in: A. E. Nordenskiold, Studier och Forskningar, Stockholm, 1S83.) 



