462 



ISLAND LIFE. 



[part ir. 



Nearly 500 of its species are identical with Indian or Malayan 

 plants, or are very close representatives of them ; while there 

 are more than 200 Indian genera, confined for the most part to 

 the tropical portion of Australia. The remainder of the tro- 

 pical flora consists of certain species and genera of temperate 

 Australia which range over the whole continent, but these 

 form a very small portion of the peculiarly Australian genera. 



These remarkable facts clearly point to one conclusion — that 

 the flora of tropical Australia is, comparatively, recent and 

 derivative. If we imagine the greater part of North Australia 

 to have been submerged beneath the ocean, from which 

 it rose in the middle or latter part of the Tertiary period, 

 offering an extensive 9.rea ready to be covered by such suitable 

 forms of vegetation as could first reach it, something like the 

 present condition of things would inevitably arise. From the 

 north widespread Indian and Malay plants would quickly 

 enter, v/hile from the south the most dominant forms of tem- 

 perate Australia, and such as were best adapted to the tropical 

 climate and arid soil, would intermingle with them. Even if 

 numerous islands had occupied the area of Northern Australia 

 for long periods anterior to the final elevation, very much the 

 same state of things would result. 



The existence in North and North-east Australia of enormous 

 areas covered with Cretaceous and other Secondary deposits, as 

 well as extensive Tertiary formations, lends support to the view, 

 that during very long epochs temperate Australia was cut off 

 from all close connection with the tropical and northern lands 

 by a wide extent of sea ; and this isolation is exactly what was 

 required, in order to bring about the wonderful amount of 

 specialisation and the high development manifested by the 



species than the former." This, however, appears to me to be hardly a 

 case in point, because Europe is a distinct continent from Africa and has 

 had a very different past history. A closer parallel may perhaps be found 

 in equal areas of Brazil and south temperate America, or of Mexico and 

 the Southern United States, in both of which cases I suppose there can be 

 little doubt that the tropical areas are far the richest. Temperate South 

 Africa is, no doubt, always quoted as richer than an equal area of tropical 

 Africa or perhaps than any part of the world of equal extent, but this is 

 admitted to be an exceptional case. 



