530 ISLAND LIFE part ii 



in the flora of Australia and its relation to that of New 

 Zealand. 



In the more general explanation of the relations of the 

 various northern and southern floras, I have shown what 

 an important aid to any such explanation is the theory of 

 repeated changes of climate, not necessarily of great 

 amount, given in Chapters VIII. and IX. ; while the whole 

 discussion justifies the importance attached to the theory 

 of the general permanence of continents and oceans, as 

 demonstrated in Chapter VI., since any rational explana- 

 tion based upon facts (as opposed to mere unsupported 

 conjecture) must take such general permanence as a 

 starting-point. The whole inquiry into the phenomena 

 presented by islands, which forms the main subject of the 

 present volume, has, I think, shown that this theory does 

 affords a firm foundation for the discussion of questions 

 of distribution and dispersal ; and that by its aid, com- 

 bined with a clear perception of the wonderful powers 

 of dispersion and modification in the organic world when 

 long periods are considered, the most difficult problems 

 connected with this subject cease to be insoluble. 



