1868.] HOOKER— ARCTIC FLORA. 335 



In one respect this migration is most direct in the American 

 meridian, where more arctic species reach the highest southern 

 latitudes. This I have accounted for (Flora Antarctica, p. 230) 

 by the continuous chain of the Andes having favoured their 

 southern dispersion. 



But the greatest number of arctic plants are located in Central 

 Europe, no fewer than 530 out of 762 inhabiting the Alps and 

 Central and Southern Europe, of which 480 cross the Alps to the 

 Mediterranean basin. Here, however, their further spread is 

 apparently suddenly arrested ; for though many, doubtless, are to 

 be found in the Alps of Abyssinia and the western Atlas; these 

 are few compared with what are found further east in Asia ; and 

 fewer still have found their way to South Africa. 



The most continuous extension of Scandinavian forms is in the 

 direction of the greatest continental extension; namely that from 

 the North Cape in Lapland to Tasmania* ; for no less than 350 

 Scandinavian plants have been found in the Himalaya, and 53 in 

 Australia and New Zealand ; whereas there are scarcely any 

 Himalayan and no Australian or Antarctic forms in Arctic 

 Europe. Now that Mr. Darwin's hypotheses are so far accepted 

 by many botanists, in that these concede many species of each 

 genus to have had in most cases a common origin, it may be well 

 to tabulate the generic distribution of arctic plants as I have done 

 the specific ; and this places the prevalence of • the Scandinavian 

 types of vegetation in a much stronger light : — 



Scandinavian Arctic Genera in Europe. . 2S0 Cross Alps (approximately) 260 



Found in N. U. S. (approximately)... 270 Found in South Africa (approximately) no 



" Tropical American Mts. " ... 100 ; " Himalaya, etc 270 



" Temperate South America 4i ... 120 " Tropical Asia So 



•• Alps " ... 2S0 " Australia, etc 100 



The most remarkable anomaly is the absence of Primula in 

 Tropical America, that genus being found in Extra-tropical South 



* The line which joins these points passes through Siberia, Eastern 



China, the Celebes Islands, and Australia, hut the glacial migration has 

 no doubt been due south from the arctic and north temperate regions in 

 various longitudes to the Pyrenees, Alps, Carpathians, Caucasus, Asia 

 Minor, Persian and North Indian mountains, etc. The further migration 

 south to the distant and scattered alpine heights of the tropics, and thence 

 to South Australia, Tasmania, and New Zealand, is, in the present state 

 of our knowledge, to me quite unaccounted for. Mr. Darwin assumes for 

 this purpose a cooled condition of the globe that must have been fatal 

 to all such purely tropical vegetation as we are now familiar with. 



