526 ALTERATION IN FLORA SINCE 



throughout ; . . . and in New Zealand and the Antarctic Islands, many of 

 the species remaining unchanged throughout. 



Darwin in the Origin of Species states that : 

 from the extraordinary manner in which European productions have 

 recently spread over New Zealand, and have seized on places which must 

 have been previously occupied, we may believe, if all the animals and 

 plants of Great Britain were set free in New Zealand, that in the course 

 of time a multitude of British forms would become thoroughly naturalised 

 there, and would exterminate many of the natives. On the other hand, 

 from what we see now occurring in New Zealand, and from hardly a 

 single inhabitant of the southern hemisphere having become wild in any 

 part of Europe, we may doubt, if all the productions of New Zealand were 

 set free in Great Britain, whether any considerable number would be 

 enabled to seize on places now occupied by our native plants and animals. 



Arguing from the facts advanced by Sir J. D. Hooker, A. R. 

 Wallace in Island Life (1880) has discussed the question at some 

 length, and I quote that portion of his remarks which bears directly 

 on the New Zealand flora. He says (p. 479): 



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 established 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 develop- 

 ment 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 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. 



Wallace was very strongly impressed by several instances of the 

 rapid spread of European plants in New Zealand which had been 

 communicated to him by Enys, Travers, and other good observers. 

 Some of the examples given by Wallace in Darwinism may be referred 

 to here. Thus he gives instances of the spread of water-cress in the 

 streams of the Canterbury Plains ; of white clover displacing native 

 species and even exterminating the native flax (Phormium tenax) ; of 

 Hypochceris radicata (the so-called Cape-weed of the South Island) : 



which destroyed excellent pasture in three years, and absolutely displaced 

 every other plant on the ground. It grows on every kind of soil, and is 

 even said to drive out the white clover, which is usually so powerful 

 in taking possession of the soil ; 



of knot-grass {Polygonum aviculare), common 6.oc\i {Rumex obttisi- 

 folius), sowthistle {Sonchus oleraceus) and sorrel {Rumex acetosella). 



