462 
ISLAND LIFE. 
[pabt 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 area 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, while 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. 
