Australian Flowering Plants. 201 



with local secondary developments in America, South Africa, 

 Australia, and the Northern Hemisphere. The endemic secon- 

 dary forms in South Africa and Australia are xerophytes. The 

 primary type is characteristically a tree with a beautiful 

 appearance, possessing pinnate leaves, and a lover of mild 

 and moist climatic conditions. 



After the isolation of Australia from the great tropical lands, 

 and the zoning of climates, the luxuriant Rutacese in that 

 country found themselves faced with the great problem which 

 had confronted the megathermic Leguminosse and Myrtacese, 

 namely, the possibility of being forced to retreat, defeated, to 

 the narrow belt of coastal area possessing mild and moist con- 

 ditions, or of accommodating themselves to the new conditions. 



They had the hungry, sandy soils upon which to make 

 experiments and they possessed a stock of essential oil glands 

 in the leaves, and other parts of the plants, wherewith to 

 check excessive transpiration during the slow desiccation of 

 Australia. Like the Leguminosse and the Myrtaceas, they 

 made use of the great areas of hungry, sandy soils, and by a 

 gradual process of reduction in size of the individual from 

 trees to shrubs, to undershrubs and herbs, they produced the 

 large endemic tribe Boroniete with 18 genera and about 180 

 species. The leaf surface was also much reduced, and the 

 primitive luxuriant pinnate leaf has been changed in Boronieae 

 to small, simple, trifoliolate, or rarely pinnate types. 



The sandy wastes and the sandstone areas contain nearly 

 the whole of this large endemic tribe. 



In South Africa, a similar development took place, where 

 the old luxuriant Xanthoxylese produced the large endemic 

 tribe Diosmese in 3 subtribes, the number of genera being 11 

 with from 185 to 200 species. As in Australia the development 

 took place mainly on the hungry, sandy tracts of land lying 

 within the temperate region and the resulting endemic tribe 

 is markedly xerophytic. Each country presents a remarkable 

 example of the local development of secondary types from the 

 primitive Xanthoxylese in hungry, sandy soils in dry hot 

 summer regions, the areas being isolated, however, during the 

 parallel evolution. As in Australia also the secondary types 

 were shrubs, undershrubs, and rarely herbs. 



In tropical America, another endemic tribe, namely Cus- 

 pariete, was developed, with about 16 genera and with 85 to 

 90 species. 



In the fertile and warm areas of Eastern Australia the 

 primary Xanthoxylese developed about 5 endemic genera, but 



