Australian Flowering Plants. 197 



spread of root at the zone of moisture, and on the relative lack 

 of nitrogenous, calcareous, and allied nutriment in the sands. 

 The types thus evolved were exceedingly hardy and became 

 vigorous and aggressive with the usual result, namely, the 

 production of numerous genera and species. Hence during 

 the double period of climatic differentiation the first of which 

 occurred while all the great lands were in some close connec- 

 tion, the second after the isolation of the great tropical lands, 

 the 19 or 20 genera and about 400 species of the Australian 

 Podalyriese appear to have been developed. 



In South Africa, on the hungry Mesozoic sandstones, and in 

 a climatic environment somewhat similar to that of Australia, 

 the Podalyriese of that region arose. In South America the 

 conditions which obtained in South Africa and in Australia 

 were not existent, and moreover, a more severe competition 

 arose owing to the ingress of aggressive northern types, whereas 

 South Africa, on the one hand, was protected by a barrier from 

 northern competition, while Australia was protected by the 

 ocean. 



The story of the Genistese is perhaps even more interesting. 

 It is supposed by Bentham that Podalyriese is related more 

 closely to Genistese than to Sophorese, and this may, perhaps, 

 be so, 15 owing to certain peculiarities of habit and foliage 

 common to the tribes, nevertheless the bloom is nearer Sophorese 

 than Genistese. In the tropics the Genistese have almost van- 

 ished, with the exception of the great genus Crotalaria (300 

 species). In its early days, the Genistese, like Acacia, were 

 more given to populate open places than the jungle, hence their 

 extinction, in part, in the dry tropics. 



In the Northern Hemisphere, the Genistese retained the 



traces of the old arborescent habit more than did the northern 



Podalyriese and by reduction of size, and the rejection of 



foliage, in great part they held their own, and developed new 



and aggressive genera such as Ulex, Genista, Spartium, and 



Lupinus. In Australia the hungry, sandy soils gave them a 



chance, and new genera, such as the peculiar and vigorous 



tribe Bossiaese, were developed on the sandy and rocky wastes 



both as shrubs and undershrubs, with small leaves or with 



none. But the tribe never flourished in Australia as did the 



Podalyriese. In South Africa, however, on the hungry, sandy 



soils, the tribe developed enormously with great aggressive 



genera such as Aspalathus (above 150 species). 



15 If this be so then Podalyriese has had a parallel development with 

 Sophorese and with Genistese. 



