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Show 490 ISLAND LIFE. (PART II. a group of large islands probably extends across or aro~nd the south polar area to Victoria Land and thenc.e to .Adehe Land. Tl1 e ou tly m· g Younoo- Island ' 12 ' 000 feet. htgb, IS abou'td 750d miles south of the Macquarie Islands, wbwh may be cons1 ere a southern outlier of the New Zealan~ gro~1p; and the Mac- quan.e Islands are about the same distance from the 1,000- ~ · f T £a th om l1. n e , markinoo- the probable southern extensdi'O n o · as-mania. Other islandR may have existed at interme Iate pomts; but even as it is, these distances are not greater than we know are 'traversed by plants both by flotation and by aerial current~, especially in such a stormy atmosphere as that of the Antarctic regions. Now, we may further assume, that wha~ we know occurred within the Arctic circle also took place m the Antarctic- that is, that there have been alternations of climate during which some portion of what are now ice-clad lands became able to support a considerable amount of vegetation.1 During such periods there would be a s~eady migration of plants from all southern circumpolar countnes to people the comparatively unoccupied continent, and the southern .ex~remity of America being considerably the nearest, and also bcmg the best stocked with those northern types which have such great powers of migration and colonisation, such .plants wou~d form the bulk of the Antarctic vegetation, and durmg the contmuance of the milder southern climate would occupy the whole area. When the cold returned and the land again became ice-clad, these plants would be crowded towards the outer margins of the Antarctic land and its islands, and some of them would find their way across the sea to such countries as offered on their mountain summits suitable cool stations; and as this process of alternately irecei:ving plants from Chile and Fuegia and transmittino- them in all directions from the central Antarctic land may have been repeated several times during the Tertiary period, we have no difficulty in understanding the g-eneral com- 1 The recent discovery of a rich flora on rocky peaks rising out of the continental ice of Greenland, as well as the abundant vegetation of tl:e highest northern latitudes, renders it possible tha~ even now th~ Ant~rctw continent may not be wholly destitute of vegetatiOn, although 1ts. chmute and physical condition nre far less favourable than thoRe of the Arct1e lands. cnAP. xxm.] AUCTIC PLANTS IN NEW ZEALAND. 491 :g1unity between the European and Antarctic plants found in all south temperate lands. Kerguelen's Land and The Crozets are within about the same distance from the Antarctic continent as New Zealand and Tasmania, and we need not therefore be surprised at finding in each of these islands some Fuegian species which have not reached the others. Of course there will remain difficulties of detail, as there always must when we know so imperfectly the past changes of the earth's surface and the history of the particular plants concerned. Sir Joseph Hooker notes, for example, the curious fact that several Compositre common to three such remote localities as the Auckland Islands, Fuegia, and Kerguelen's Land, have no pappus or seed-down, while such as have pappus are in no case common even to two of these islands. Without knowing the exact history and distribution of the genera to which these plants belong it would be useless to offer any conjecture, except that they are ancient forms which may have survived great geographical changes, or may have some peculiar a.nd exceptional means of dispersion. Proofs of Migration by way of .the Himalayas and Southern Asia.-But although we may thus explain the presence of a considerable portion of the European clement in the floras of New Zealand and Australia, we cannot account for the whole of it by this means, because Australia · itself contains a host of European and Asiatic genera of which we find no trace in New Zealand or South America, or any other Antarctic land. We find, in fact, in Australia two distinct sets of European plants. First we have a number of species identical with those .of Northern Europe or Asia (of the most characteristic of which-thirty-eight in number-Sir Joseph Hooker gives a list); and in the second place a series of European genera usually of a somewhat more southern character, mostly represented by very distinct species, and all absent from New Zealand; such as Clematis, Papaver, Cleome, Polygala, Lavatera, A juga, &c. Now of the first set-the North European species-about three-fourths occur in some parts of America, and about half in South. Temperate America or New Zealand; whence we mny conclude that most .of tbes.e, as well as some |
