Australian Flowering Plants. 195 



vast Eurasian and American regions, and on the other hand, 

 there would not be a development along the vigorous and aggres- 

 sive lines such as might be expected in the great connected land 

 blocks of the northern hemisphere. 



In Australia there are vast expanses of coarse sandy soils 

 which have been derived, ultimately, from the great sandy 

 granites of East and West Australia — but derived, directly, in 

 great measure, from the great exposures of Mesozoic sandstones, 

 especially in Eastern Australia. 



These soils are extremely loose and porous and contain 

 moisture, almost permanent, at depths of a few yards from the 

 surface, but they contain very little moisture near the surface 

 except on the mountain sides, or in moist seasons. In dry 

 seasons this sandy soil neither becomes caked nor hard, and 

 the water level simply sinks at a very slow rate. On the dense 

 heavy soils of the slates, andesites, basalts, and allied rock 

 types, a long succession of moist and mild seasons would pro- 

 duce dense growths of luxuriant trees and vines to the exclusion 

 of xerophytes generally, but if the region should be subject 

 to great droughts and to long continued desiccating winds, 

 and to great diurnal and annual changes of temperature, then 

 this luxuriant growth would cease. In moist, mild seasons a 

 luxuriant crop of herbage would arise, especially if the seeds 

 of such hei'bage should be protected by special devices against 

 excessive loss of moisture. In the long spells of dry weather 

 this herbage would be burnt off, as it could not keep in touch 

 with the underlying water supply, owing to the tough and non- 

 porous nature of the dried upper clods of earth, while only 

 trees such as were provided with very long and deep roots, and 

 with special devices against excessive transpiration, could 

 survive. 



In the old moist and mild climate of Australia the heavier 

 soils had a dense covering of luxuriant vegetation while the 

 much greater areas of coarse, sandy soils (the central sea being 

 then very large and the existing great central black and red 

 soil plains being non-existent) were clad with mesophytic for- 

 est growths, much as may be seen to-day under similar condi- 

 tions in ]STew Zealand, northeast Queensland, and other 

 countries, while on the open plains or low plateaus of such 

 country there would be a tendency to form stunted forest 

 growths of the mesophytes. 



With the alteration of the Australian climate from mild and 

 moist and uniform to fiercely-hot and dry summers, and to 

 desolating dry winds during the winter, all this condition of 



