ac^mv 0P sconces.] HISTORY OF ALPINE FLORA. 17 



only a few of these glacial plants now inhabiting the Alpine regions have changed their aspect 

 and structure so as to exhibit a variation from their Arctic prototypes. 



Thus in defining the Arctic element of the Alpine flora of Colorado it seems natural to 

 suppose that all the circumpolar species originated in the polar regions, while some of those 

 that are merely Arctic-Alpine may have developed in the south, but accompanied their 

 Arctic brethren on their return to the north. The latter explanation is also applicable to such 

 species as are not Alpine, but which, nevertheless, are known to occur in the northern regions. 

 I think especially of CJiamaenerium angusti folium, Linnaea borealis, Draba aurea, Arabis 

 Holboellii, Pyrola secunda, Carex vulgaris, and Luzula parviflora, all of which are known from 

 subarctic Greenland. 



As regards the distribution of the Alpine species according to altitude, it is interesting to 

 see that many of those observed at the highest elevations are mostly endemic, viz, Thlaspi, 

 Lychnis, Claytonia, Trifolium nanum, Saxifraga chrysaniha, Oreoxys humilis, 0. alpina, Pole- 

 monium viscosum, Eritrichium, Mertensia alpina, Chionophila, Synthyris, and Poa Lettermannii, 

 while the remaining Saxifraga flagellaris, S. nivalis, S. cernua, Lloydia, etc., extend to the 

 Arctic regions and to the higher mountains in Europe and Asia. Chionophila is monotypic; 

 of Synthyris and Oreoxys, only a very few species are known, and these three genera are confined 

 to North America; the other genera are cosmopolitan. At lower elevations, but still in the 

 Alpine region, we meet with a number of species that are endemic to North America, and of 

 these several are confined to this region and may be looked upon as representing an old Alpine 

 vegetation. On the other hand, several of the Alpine species have descended to the wooded 

 belts, the spruce, as well as the aspen zone, where they are now frequently appearing in a more 

 or less specific disguise. Finally, it deserves notice that a pronounced lowland element does 

 exist at high elevations in these mountains, consisting of species which may have accompanied 

 the Arctic on their way to the summits. Among these are: Potentilla fruticosa, Kalmia, Arcto- 

 staphylos, Vaccinium Myrtillus, Campanula rotundifolia, Troxhnon, Achillea, Pentstemon 

 confertus, P. glaueus, Pedicularis Groenlandica, Deschampsia caespitosa, and Calamagrostis 

 Canadensis. 



The Alpine vegetation thus comprises four distinct elements, viz: Circumpolar, Arctic, 

 Alpine, and lowland species. 



