i66 NOTES OF A NATURALIST. 



been a little sceptical as to the primary importance 

 attributed by Darwin * to the fact that most of these 

 invaders are northern continental species. In the 

 course of a long existence extending over wide areas, 

 he maintains that these have acquired an organization 

 iitting them better to maintain the struggle for exist- 

 ence than the indigenous species of the regions oyer 

 which they have spread. Of course, it is true in the 

 case of territories very recently raised from the sea, 

 and not in direct connection with a continental area 

 inhabited by species well adapted to the conditions of 

 soil and climate, that immigrant species well adapted 

 to the conditions of their new home will spread very 

 rapidly, and may easily supplant the less vigorous, 

 because less well adapted, native species. The most 

 remarkable case of this kind is perhaps presented by 

 Northern Patagonia and a portion of the Argentine 

 region, raised from the sea during the most recent 

 geological period. The only quarters from which the 

 flora could be recruited were the range of the Andes 

 to the west, and the subtropical zone of South 

 America to the north. Everything goes to prove that 

 the forms of plants are far more slowly modified than 

 those of animals — or, at least, of the higher vertebrate 

 orders. The new settlers are unable quickly to adapt 

 themselves to the new conditions of life, and as a 

 result we find that the indigenous flora of the region 

 in question is both numerically poor in species, and 

 that these have been unable fully to occupy the ground. 

 Among the species intentionally or accidentally intro- 

 duced by the European conquerors, those well adapted 

 * " Origin of Species," 3rd edit., p. 410. 



