CHAP. XXIII ARCTIC PLANTS IN NEW ZEALAND 511 



associated with alpine forms of Germanic, Siberian, Oriental, 

 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." ^ 



It is impossible to place the main facts more forcibly 

 before the reader than in the above striking passage. It 

 shows clearly that this portion of the New Zealand flora is 

 due to wide-spread causes which have acted with even 

 greater efl*ect 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. 



Aggressive Power of the Scandinavian Flora. — 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 in New Zealand, 

 often taking possession of large 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 how import- 

 ant 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 dis- 

 ^ Introductory Essay On the Flora of Australia^ p. 130, 



