532 ALTERATION IN FLORA SINCE 



This supposition will also throw some light on the curious fact that 

 the vast majority of our plants are of northern origin. It is now generally 

 admitted by geologists that the present continents are of immense 

 antiquity, and that there has been no great alteration in the relative pro- 

 portions of land and water during vast geological epochs. Mr Darwin 

 therefore argues that as the northern hemisphere has probably always 

 possessed the most extensive continuous land area, so the wonderfully 

 aggressive and colonizing power of its plants at the present time is due 

 to development where the competition of species has been the most severe 

 and long continued, owing to the presence of facilities for natural migration. 

 The plants of the comparatively isolated countries of the southern hemi- 

 sphere have not been subjected to the same degree of competition, and 

 consequently could not be so advantageously modified. 



Mr Kirk, who paid special attention to the naturalisation of plants 

 in New Zealand, in a paper on the naturalised plants of Port Nicholson > 

 says: 



At length a turning-point is reached, the invaders lose a portion of 

 their vigour and become less encroaching, while the indigenous plants 

 find the struggle less severe and gradually recover a portion of their lost 

 ground, the result being the gradual amalgamation of those kinds best 

 adapted to hold their own in the struggle for existence with the introduced 

 forms, and the restriction of those less favourably adapted to habitats 

 which afford them special advantages. 



Further on in the same article Mr Kirk combats the view that the 

 majority of our native plants will become extinct, stating that the 

 particular species for which this danger is to be feared might almost 

 be counted upon one's fingers. 



My own views on this difficult question are much nearer to 

 Mr Kirk's than to those of Mr Travers. I can certainly find little 

 evidence in support of the opinion that a considerable proportion of 

 the native flora will become extinct. Even in isolated localities of 

 limited areas, like Madeira and St Helena, where there is little variety 

 of climate and physical conditions, and where the native plants have 

 been subjected to far more disadvantageous influences, and to a 

 keener competition with introduced forms than in New Zealand, the 

 process of naturalisation has not gone so far as to stamp out the whole 

 of the indigenous vegetation, although great and remarkable changes 

 have been effected, and many species have become extinct. I fail to 

 see why it is assumed that a greater effect will be produced in New 

 Zealand, with its diversified physical features and many varieties of 

 soil, situation, and climate. Surely its far-stretching coast-line, bold 

 cliffs, and extensive sand-dunes, its swamps and moorlands, its lofty 

 mountains and wide-spreading forests, will afford numerous places of 

 refuge for its plants until sufficient time has been allowed for the 

 gradual development of varieties better suited to the changed con- 



