viiAV. XXIV SUMMARY AND COXCLUSIOX 543 



as to present in Sir Joseph Hooker's opinion an almost 

 insoluble problem. Much additional information on the 

 l^hysical and geological history of these two countries has, 

 however, been obtained since the appearance of Sir Joseph 

 Hooker's works, and I therefore determined to apjDly to 

 them the same method of discussion and treatment which 

 has been usually successful with similar problems in the 

 case of animals. The fact above noted, that New Zealand 

 was connected with Australia in its northern and tropical 

 portion only, of itself affords a clue to one portion of the 

 specialities of the New Zealand flora — the presence 

 of an unusual number of tropical families and genera, 

 while the temperate forms consist mainly of species either 

 identical with those found in Australia or closely allied to 

 them. But a still more important clue is obtained in the 

 geological structure of Australia itself, which is shown to 

 have been for long periods divided into an eastern and 

 a western island, in the latter of Avhich the highly peculiar 

 flora of temperate Australia was developed. This is found 

 to explain with gTeat exactness the remarkable absence 

 from New Zealand of all the most abundant and 

 characteristic Australian genera, both of plants and of 

 animals, since these existed at that time only in the 

 vjestcrn island, while New Zealand was in connection with 

 the eastern island alone and with the tropical portion of 

 it. From these geological and physical facts, and the 

 known powers of dispersal of plants, all the main features, 

 and many of the detailed peculiarities of the New Zealand 

 flora are shown necessarily to result. 



Our last chapter is devoted to a wider, and if possible 

 more interesting subject — the origin of the European 

 element in the floras of New Zealand and Australia, and 

 also in those of South America and South Africa. This is 

 so especially a botanical question, that it was with some 

 diflidence I entered upon it, yet it arose so naturally from 

 the study of the New Zealand and Australian floras, and 

 seemed to have so much light thrown upon it by our 

 preliminary studies as to changes of climate and the causes 

 which have favoured the distribution of plants, that I felt 

 my work would be incomplete without a consideration of 



