HOOKER ON ARCTIC PLANTS. 207 



by the continuous chain of the Andes having favom-ed 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, there 

 are few compared with what we 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 Himalayas, and 53 in 

 Australia and New Zealand, whereas there are scarcely any Hima- 

 layan and no Australian or Antarctic forms in Ai'ctic 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 the 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 - - - 280 



Found in North-United- States - - (approximately) 270 



„ Tropical American mountains „ 100 



„ Temperate South America - „ 120 



„ Alps- ... - - „ 280 



Cross Alps „ 260 



Found in South Africa - - - ^^ 1 10 



„ Himalaya, &c. - - - ,, 270 



,, Tropical Asia - - _ ^^ 80 



„ Australia, &c. - - - ^^ 100 



The most remarkable anomaly is the absence of Primula in 

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

 America, and its absence in the]whole Southern Temperate zone of 

 the Old World, except the Alps of Java. 



Thalictrum, Delphinium, Impatiens, Prunus, Circcea, Chryso- 

 spleniu7n, Parnassia, Bupleururn, Hieracleum, Viburnum, Vale- 

 riana, Artemisia, Vaccinium, Rhododendron, Pedicularis, and 

 Salix are all Arctic Genera found on the Tropical mountains of 

 Asia (Nilghiri, Ceylon, Java, &c.), but not yet in the South- tem- 



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

 the Celebes Islands, and Australia ; but the glacial migration has been due 

 south from the Arctic and North-temperate regions in various longitudes to the 

 Pyrenees, Alps, Carpathians, Caucasus, Asia Minor, and the Persian and North- 

 Indian mountains. 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 unac- 

 counted for. Mr. Darwin assumes for this purpose a cooled condition of the 

 globe that must have been fatal to all such purely tro]>ical vegetation as we 

 iire now familiar with. 



