202 E. C. Andrews — The Geological History of the 



with the exception of the oligotypic Melicope, these genera are 

 practically monotypic and quite unlike the aggressive and 

 vigorous Boronies9. 



In the northern hemisphere another tribe, the Rutea?, was 

 developed, but whether these were hardy secondary types of 

 Xanthoxyleic or a northern modification of another tribe, allied 

 to Xanthoxylere, the writer is unable to say, owing to non- 

 acquaintance with the tribe Ruteae. 



The Toddaliese and the Aurantiaceaa might, perhaps, for the 

 purpose of geographical distribution, better be considered as 

 separate families, much as Stellate, in Rubiacese, would be 

 considered better as a family distinct from Rubiacese. 



The Malpighiaceas, Meliacese, Burseracese, and Simaru- 

 bacese, are all close allies of Rutacese and their distribution is 

 similar to that of Rutacese, except that the Rutaceae with their 

 essential oil content have been more elastic in accommodating 

 themselves to harsh extratropical conditions. 



Similar evidence is supplied by a study of the Euphorbiacese, 

 Labiatae, Verbenaceae, Sterculiacese, SapindaceaB, Apocynacese, 

 Asclepiadacea?, Pittosporacese, Tremandracea?, Liliacese, Orchi- 

 dacea?, and other families. The remarkable cases of the 

 Proteacese and the Epacridacese are considered subsequently 

 under other heads. 



In nearly every case it has been the hungry, sandy soils 

 which have formed the areas on which the distinctive develop- 

 ments have been conducted during the climatic zoning after 

 the isolation of Australia. In every case the primary types 

 are luxuriant and cosmopolitan in the tropics ; in almost every 

 case the endemic tribe, genus, or species, has been dependent 

 for its existence, or its development, on the hungry, sandy soils. 

 In nearly every case the development has been markedly 

 extratropical, and in every case the new groups, whether 

 myrtaceous, leguminous, rutaceous, euphorbiaceous, verbena- 

 ceous, lamiaceous, or other angiospermous form, is xerophytic. 

 In every case the tropical family from which the xerophytes 

 have sprung has possessed some peevdiar virtue, or principle, 

 by which the family has been enabled to survive during the 

 gradual process of desiccation, and during the interval neces- 

 sary to reduce the tree size, the form, the leaf area, and so on. 

 In the Legumes it was the ability to dispense with leaves, the 

 ability to develop gums, and so on ; in Myrtacese it was the pres- 

 ence of much essential oil, the development of capsular fruits 

 and the reduction of leaf and of plant size ; in Rntacese, it was 

 the presence of abundant essential oil ; in Euphorbiaceae, it was 



