THE VICTORIAN NATURALIST. ^^^B 1^7 



sources — (a) Oriental, dominant in tropical Australia; (b) Andean, 

 restricted generally to high parts of Tasmania, Victoria, and New 

 South Wales. (2) An endemic part, a localized type of which 

 occupies the extreme south-west of the continent. The New 

 Zealand flora has also South American, European, and Antarctic 

 affinities. One-eighth of its flora is South American, and one- 

 quarter Australian; but, strange to say, it has not those most 

 highly characteristic Australian forms — Acacia, Eucalyptus, 

 GreviUea, and Hakea, these are entirely wanting. If we follow 

 Professor Tate's account of the flora we will be better able to 

 understand its distribution. He divides it into three types — (i) 

 Euronotian ; (2) Autochthonian ; (3) Eremian. If we pass from 

 the coast to the interior, we pass from timbered grass land and 

 forest land to a grass growth with a few shrubs, and beyond this 

 the vegetation is strikingly dissimilar — it is the so-called saltbush 

 country. This variation in botany is co-ordinate with a decreas- 

 ing rainfall — thus, at Port Darwin the rainfall is from 50 to 75 

 inches ; on the east coast, from 25 to 50 inches ; in south-west, 

 from 25 to 50 inches ; but in the interior — that is, the saltbush 

 country — we find it less than ten inches, (i) Euronotian in south 

 and east. (2) Autochthonian in south-west; it coincides with a 

 rainfall limit of 20 inches. (3) Eremian, dominant in dry region 

 which has its centre in the Lake Eyre basin ; it corresponds with 

 saltbush country, and has rainfall of less than 10 inches. 



The Autochthonian type of vegetation extends from Shark Bay 

 to Cape Arid. The maximum rainfall is 46 inches. This region 

 is smaller than the eastern, with no lofty mountains, and with 

 deserts, yet it contains a far greater proportion of peculiar plants 

 than the east. In purely Australian types it is far richer than 

 the rest of the continent. This large and peculiar flora implies 

 long-continued isolation. What physical causes have brought 

 about and maintained that isolation ? What are the barriers that 

 have prevented the spread of this flora to the east ? For in the 

 Euronotian, though we do find many Australian types, they are 

 mixed with European, Antarctic, and South American types, and 

 many of the chief Australian types are wanting here. The 

 Eremian region itself is, and always has been, the barrier. This 

 botanic region has its centre at Lake Eyre, where the average 

 rainfall is less than 5 inches ; but the region is not a desert. It 

 occupies an excessively dry region, which is an impassable barrier 

 to the interchange of Autochthonian and Euronotian types. 

 The only way of migration may have been by extension of 

 south coast line in post-Miocene times. This climatic barrier has 

 not always existed, for in Cretaceous times a large part of the 

 east of this region was a bed of sea. South-west Australia is 

 the remnant of a more extensive part of the continent. If we 

 take ths i, coo-fathom line around the southern part of Australia 



