CHAP. XXIII ARCTIC PLANTS IN XEAV ZEALAND 529 



Concluding Remarks on the Last Tiuo Chapters. — Our 

 inquiry into the external relations and probable origin of 

 the fauna and flora of New Zealand, has thus led us on to 

 a general theor}^ as to the cause of the peculiar biological 

 relations between the northern and the southern hemi- 

 spheres ; and no better or more typical example could 

 be found of the Avide range and great interest of the 

 study of the geographical distribution of animals and 

 plants. 



The solution which has here been given of one of the 

 most difficult of this class of problems, has been rendered 

 possible solely by the knowledge very recently obtained 

 of the form of the sea-bottom in the southern ocean, and 

 of the geological structure of the great Australian continent. 

 Without this knowledge we should have nothing but a 

 series of guesses or probabilities on which to found our 

 hypothetical explanation, which we have now been able 

 to build up on a solid foundation of fact. The complete 

 separation of East from West Australia during a portion of 

 the Cretaceous and Tertiary periods, could never have been 

 guessed till it was established by the laborious explorations 

 of the Australian geologists ; while the hypothesis of a com- 

 paratively shallow sea, uniting New Zealand by a long route 

 with tropical Australia, while a profoundly deep ocean 

 always separated it from temperate Australia, would have 

 been rejected as too improbable a supposition for the 

 foundation of even the most enticing theory. Yet it is 

 mainly by means of these two facts, that we are enabled 

 to give an adequate explanation of the strange anomalies 

 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 VL, since any rational explana- 

 tion based upon facts (as opposed to mere unsupported 



