Australian Flowering Plants. 205 



epiphytes had become terrestrial owing to the severe and harsh 

 climatic conditions existing in the extratropical sandy wastes of 

 eastern Australia. In short the trees no longer afforded them 

 the necessary protection, whereupon they descended and were 

 preserved in the sandy wastes by the development there of new 

 xerophytic genera. 



Of the 48 genera in Australia, 28 genera, comprising one- 

 third of the total number of species, including the whole of the 

 tribes Malaxidese, Vandese, Bletidese, Arethusese, the first group 

 of Neottidese, and the Ophrydeae, belong to the tropical Asiatic 

 Flora represented in Australia by endemic or, frequently, by 

 identical species. These are all tropical or eastern, some 

 extending down to Tasmania, but none found in West Aus- 

 tralia ; five of these genera are also in New Zealand. The 

 remaining 20 genera, comprising two-thirds of the species, are 

 essentially Australian, belonging to three Australian groups of 

 Neottidese; four of these genera are, however, represented by 

 single or very few species in the Indian Archipelago and eleven 

 have New Zealand congeners, sometimes identical in species. 21 



This closes the case for the Tropical Problem. When the 

 South African Problem shall have been discussed in connection 

 with the distribution of the families Proteacese, Epacridaceae, 

 Compositse, Campanulacese, Lobeliacea?, Groodeniacese, and Can- 

 dolleacese, it will be evident that the general position in the plant 

 world of the endemic Australian vegetation will be even more 

 apparent than it is already from the present brief statement of 

 the Tropical Problem. A careful consideration of the evidence 

 here adduced, however, in which the widespread existence in 

 the fertile tropics of luxuriant primary types, distributed 

 among vast genera, is evident, with the great local developments 

 of secondary xerophytic and depauperate forms in these families 

 within the great sandy and barren wastes of countries, such as 

 extratropical Australia and South Africa, the genera being 

 endemic in each country with very few exceptions, the morpho- 

 logical relations between the local, secondary types in the 

 several countries being less than between each secondary type, 

 the cosmopolitan primary types moreover of the tropics and these 

 endemic genera constituting the whole 22 of the great genera of 

 Australia, the same genera being also extremely hardy, vigorous, 

 and aggressive, leads to the inevitable conclusion that the vast 

 genera of the tropics have developed .their existing species in 

 situ after the isolation from each other of the old mild and moist 



21 G. Bentham, Flora Australiensis, vol. vi. pp. 268-269, 1873. 



22 Excepting the Proteaceae, Epaeridaceae, Goodeniacese and Candolleacese, 

 about to be described. 



