314 PROCEEDINGS OF SECTION D. 



basaltic patches, which also have certain distinctive botanical 

 features, as pointed out by Baron Sir F. von Mueller as far back 

 as 1855. 



From lists of species of tropical South Australia, which I have 

 compiled and drawn up according to the occurrences within the 

 area of the northern rivers, and on the tal)le land and its southern 

 extension, I present a few summarisations. 



Total Species — 1,405; in Arnheim Land 1,221, 780 of which, 

 or 63.9 per cent, are endemic; in the 1 able-land 614, of which 

 491, or 80 per cent, are endeadc. 



Sequence of the orders according to the number of species : — 



On proceeding from the coast line towards the interior of the 

 Continent, the following phytographic characteristics are observ- 

 able : — The littoral region in its lower level is a savana, tliat is 

 timbered grass-lands, and in its higher level is sylvan or forest- 

 land ; as we pass inland the timber growth on both zones becomes 

 less and less, one species after another altogether ceasing ; and 

 finally a grass growth with some shrubs dominate the surface. 

 Beyond this latter belt, the vegetation is strikingly dissimilar, 

 and shrubby salsolaceous plants, Eremophilas and Cassias are in 

 the ascendant in this so-called " salt-bush " country. This 

 variation in the botany is co-ordinate with a decreasing rainfall, 

 and though there is no line of demarcation between one type and 

 another, yet in certain localities the transition is rapidly coincident 

 with an abrupt diminution in the rainfall as a consequence of 

 some physiographic conformation, such as a mountain range 

 trending transversely to the direction of the prevailing wind, and 

 bounded on its inner side by a depressed area. 



