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Show 478 ISLAND LIFE. [PART H. or Antarctic plants and many more which are represen~ative spec1• es, are 1.[! oun d also 1'n Tasma·n ia and in the .m ountam. s of temperate Australia; and Sir J ~seph Hooker g1ves a ~1st of th. t _ 'crht species very charactenst1c of Europe and Northern H y elo . . h' h Asia, but almost or quite unknown m.the warmer reg10n~, w 1c yet reappear in temperate Australia. Other geneta seem altogether Antarctic-that is, confined to the extre~e southe.rn 1 ds and islands· and these often have representative species inan S outhern Amer'i ca, Tasmania, and New Zealan d , wh 1'l e others occur only in one or two of these areas. Many nor.th t emperate genera also occur in the mountains .of South ~fnca. On t~e other hand, few if any of the peculiar Australian or Antarctw types have spread northwards, except some of the former which have reached the mountains of Borneo, and a few of the latter which spread along the Andes to Mexico. On these remarkable facts, of which I have given but the barest outline, Sir Joseph Hooker makes the following suggestive observations :- " When I take a comprehensive view of the vegetation of the Old World, I am struck with the appearance it presents of there beincr a continuous current of vegetation (if I may so fancifully expr~ss myself) from Scandinavia to Tasmania; along, in short, the whole extent of that arc of the terrestrial sphere which presents the greatest . c~ntinuity ~f land. In the first place Scandinavian genera, and even species, reappear everywhere from Lapland and Iceland to the tops of the Tasmanian Alps, in rapidly diminishing numbers it is true, but in vigorous development throughout. They abound on the Alps and Pyrenees, pass on to the Caucasus and Himalaya, thence they extend along the Khasia Mountains, and those of the peninsulas of India to those of Ceylon and the Malayan Archipelago (Java and Borneo), and after a hiatus of 30° they appear on the Alps of New South Wales, Victoria, and Tasmania, and beyond these a<Yain on those of New Zealand and the Antarctic 0 Islands, many of the species remaining unchanged through-out! It matters not what the vegetation of the bases and flanks of these mountains may be ; the northern species may be associa ~ed v;,'ith alpine forms of Germanic, Siberian, Oriental, CHAP. XXIII.] ARCTIC PLAN'rS IN NEW ZEALAND. 479 Chinese, American, Malayan, and finally Australian and Antarctic types; but whereas these are all, more or less, local assemblages, the Scandinavian asserts his prerogative of ubiquity from Britain to beyond its antipodes." 1 It is impossible to place the main facts more forcibly before the reader than in the above striking passage. It shows clearly tltat this portion of the New Zealand flora is due to wide-spread causes which have acted with even greater effect in other south temperate lands, and that in order to explain its origin we must grapple with the entire problem of the transfer of the north temperate flora to the southern hemisphere. Taking, therefore, the facts as given by Sir Joseph Hooker in the works already referred to, I shall discuss the whole question broadly, and shall endeavour to point out the general laws and subordinate causes that, in my opinion, have been at work in bringing about the anomalous phenomena of distribution he has done so much to make known and to elucidate. Agqressive Power of the Scandinavian Flo1·a.-The first important fact bearing upon this question is the wonderful aggressive and colonising power of the Scandinavian flora, as shown by the way in which it establishes itself in any temperate country to which it may gain access. About 150 species have thus established themselves inN ew Zealand, often taking possession oflarge tracts of country; about the same number are found in Australia, and nearly as many in the Atlantic states of America, where they form the commonest weeds. Whether or not we accept Mr. Darwin's explanation of this power as due to development in the most extensive land area of the globe where competition has been most severe and long-continued, the fact of the existence of this power remains, and we can see bow important an agent it must be in the formation of the floras of any lands to which these aggressive plants have been able to gain access. But not only are these plants pre-eminently capable of holding their own in any temperate country in the world, but they also have exceptional powers of migration and dispersal over seas and oceans. This is especially well shown by the case of the Azores, where no less than 400 out of a total of 478 flowering plants are 1 Introductory Essay On the Flora of Australia, p.103. |