PT. I, CH. Ill] SPREAD OF FOREIGN SPECIES 25 



evidence was accepted without being always subjected to proper 

 sifting, and it was for a long time believed that these introduc- 

 tions spread with this rapidity and success because they came 

 from large continental areas (chiefly Europe and tropical 

 America) where they had, so to speak, become highly efficient 

 and "up-to-date" by competing in the struggle for existence 

 amongst a large crowd of other species, and were in consequence 

 exterminating the native productions because these had not 

 had such advantages. In a comparatively short time the fact 

 that introductions also occurred on continental areas was almost 

 lost sight of, and the argument was applied almost entirely to 

 islands. Darwin, for example, states (23, p. 340) that " in many 

 islands the native productions are nearly equalled, or even out- 

 numbered, by those which have become naturalised; and this is 

 the first stage towards their extinction." Wallace (111, p. 527) 

 makes very similar statements. 



Now the fact of rapid spread in many cases is undeniable, and 

 also that it has been largely, if not mainly, recorded from islands. 

 But no proper analysis of the evidence has been made. One 

 soon finds that introductions are just as common on continental 

 areas, especially where these (as was nearly always the case upon 

 islands) were untouched forest at the time of settlement. Thus 

 141 species have been recorded as spontaneous in the Transvaal, 

 S68 in South AustraHa, 364 in Victoria; 800 introductions, of 

 which 107 have become naturalised, occur near Montpellier, and 

 548 in the Tweed valley (14, 11, 35, 107, 143). One also finds 

 that the cases of rapid spread without alteration of the conditions 

 are very few indeed ; in most cases man has removed the forest, 

 made great clearances, introduced grazing animals, or in other 

 ways completely altered the circumstances, thus enabling those 

 introductions to survive and prosper which were suited to the 

 new conditions. And one further finds that when introductions 

 have spread, it has been just as much, if at all, at the expense 

 of species in the native flora that are of wide distribution as of 

 species of the most strictly local kind. The great bulk of cases 

 of spread of introductions are due, not to the fact of their having 

 come from Europe or America, but to the fact of their suiting 

 the new conditions created by clearance of the forest, or cultiva- 

 tion of the ground, to which there were few or no native species 

 suitable, and to the fact that man has thus broken up the old 

 associations of plants that covered the ground, and made it 

 possible for new plants easily to gain a foothold. In Ceylon, for 



