DISTRIBUTION OF ARCTIC PLANTS. 345 



Lapland over that of other arctic regions by the blend- 

 ing of warm and cold currents of air and water, and its 

 great diversity of mountains and lowlands ; while on the 

 broad plains of Siberia and the level plateau of Labrador 

 there is the greatest uniformity of climate, and hence a 

 corresponding paucity of plants. 



The same climatic conditions determine the distribu- 

 tion of marine life. As we go from Norway to Green- 

 land the number of species lessens greatly. Dr. Liltken, 

 in his admirable View of the Echinoderms of Green- 

 land, shows that the fauna is essentially Arctic-American 

 rather than European. It is so with the other radiates, 

 and the articulate and moUuscan fauna, and the fish 

 fauna would seem to follow the same law. 



Dr. Hooker cites fifty-seven species of plants which 

 do not cross from Greenland to America. This is par- 

 alleled by the apparent restriction of a few species of 

 marine invertebrates to the high polar seas, such as the 

 Leda truncata and Pecten grosnlandicus, though in gla- 

 cial times they abounded in northeastern America. 



Among the most purely Arctic-American plants are 

 the Potentilla tridentata, which is abundant in Green- 

 land and which we have collected in profusion in Lab- 

 rador, Maine, and on the White Mountains ; also the 

 Arenaria grcenlandica, which is more thoroughly arctic, 

 preferring the coldest spots on the outer islands of the 

 coast of Labrador, and the alpine summit of Mount 

 Washington, and which has even been detected on Cape 

 Elizabeth, Me. 



These two plants— which Dr. Hooker acknowledges 

 have never occurred elsewhere on the globe within the 

 historic period — he supposes were originally from Scan- 



