CHAP. XXIII.] ARCTIC PLANTS IN NEW ZEALAND. 



479 



Chinese, American, Malayan, and finally Australian and Ant- 

 arctic 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 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 giv^n 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 laAvs 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 impor- 

 tant 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 estab- 

 lished 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 exist- 

 ence of this power remains, and we can see how 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 

 ^ Introductory Essay On the Flora of Australia, p. 103. 



