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who have been accustomed to trust to Usher's chronology, and to look upon 

 our globe, at least, as having been created within a few thousand years, will be 

 utterly unable to accept, because they cannot comprehend, such a hypothesis. 

 But whilst each particular province presents, as I have explained to you, its 

 own peculiar generic forms, we constantly find a large degree of affinity existing 

 between the organic life occupying more extended areas comprising frequently 

 several of such provinces. Upon this point (in special connection with the 

 affinities of the flora of New Zealand) I quote as follows from Dr. Hooker's 

 "Introductory Essay" to his "Flora of New Zealand," as published in 1853 : — 



" Of all the branches of Botany, there is none whose elucidation demands 

 so much preparatory study, or so extensive an acquaintance with plants and 

 their affinities, as that of their geographical distribution. Nothing is easier 

 than to explain away all obscure phenomena of dispersion by several specula- 

 tions on the origin of species, so plausible that the superficial naturalist may 

 accept any of them ; and to test their soundness demands a comprehensive 

 knowledge of facts, which, moreover, run great risk of distortion in the hands 

 of those who do not know the value of the evidence they afford. I have 

 endeavoured to enumerate the principal facts that appear to militate against 

 the probability of the same species having originated in more places (or centres) 

 than one ; but in so doing I have only partially met the strongest argument of 

 all in favour of a plurality of centres, viz., the difficulty of otherwise accoimting 

 for the presence of two widely sundered localities of rare local species, whose 

 seeds cannot have been transported from one to the other by natural causes now 

 in operation. To take an instance, how does it happen that Edwardsia grandiflora 

 inhabits both New Zealand and South America 1 or Oxalis Magellanica both 

 these localities and Tasmania 1 The idea of transportation by aerial or oceanic 

 currents cannot be entertained, as the seeds of neither could stand exposure to 

 the salt water, and they are too heavy to be borne in the air. 



"Were these the only plants common to these widely sundered localities, 

 the possibility of some exceptional mode of transport might be admitted by 

 those disinclined to receive the doctrine of double centres ; but the elucidation 

 of the New Zealand Flora has brought up many similar instances equally 

 difficult to account for, and has developed innumerable collateral phenomena 

 of equal importance, though not of so evident appreciation. These, which all 

 bear upon the same point, may be arranged as follows : — 



"1. Seventy-seven plants are common to the three great south temperate 

 masses of land, Tasmania, New Zealand and South America. 



" 2. Comparatively few of these are universally distributed species, the 

 greater part being peculiar to the south temperate zone. 



" There are upwards of 100 genera, sub-genera, or other well marked 

 groups of plants entirely or nearly confined to New Zealand, Australia and 

 extra-tropical South America. These are represented by one or more species in 

 two or more of these countries, and they thus effect a botanical relationship or 

 affinity between them all, which every botanist appreciates. 



" 4. These three peculiarities are shared by all the islands in the south 

 temperate zone (including even Tristan d'Achuna, though placed so close to 

 Africa), between which islands the transportation of seeds is even more unlikely 

 than between the larger masses of land. 



" The plants of the Antarctic islands which are equally natives of New 

 Zealand, Tasmania, and Australia, are almost invariably found only on the 

 lofty mountains of these countries." 



The author then points out certain conclusions, to which he was at that 

 time forced by a consideration of the facts involved in the distribution of the 

 plants composing the New Zealand Flora, and proceeds as follows : — 



" It was with these conclusions before me, that I was led to speculate on 



