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



smaller in size as individuals, th.e individuals became more 

 depauperate, and more specialized, by far morphologically, 

 than the earlier Metrosiderea? and the Eucalyptus of which 

 the latter had not succeeded in reducing itself to a shrub or 

 undershrub. Nevertheless the myrtle plants never succeeded 

 in adopting the herbaceous habit. They always remained 

 either as trees, shrubs, or undershrubs. The later, more 

 depauperate and more specialized types were the subtribe 

 Ba?ckeaea? and the whole tribe Chamajlaucieae containing many 

 genera vigorous in character. 



The genera Melaleuca, Callistemon, and Leptospermum, 

 occupy a peculiar position, in that they are not so close' to 

 Myrteas as are Eucalyptus and Angophora, but their foliage 

 suggests some relation with the allied family Melastomacese. 

 These types may belong to the first great zoning of climate, 

 which is conjectured to be late Cretaceous in age. 



The essential oil in the leaves of this great family appears 

 to have been of great assistance in enabling them to adopt the 

 xerophytic habit and to populate the hungry sandy soils of 

 Australia. 



It is remarkable that nowhere else in the world do the mem- 

 bers of the Myrtacese appear to have been enabled to adapt 

 themselves well to a hot, dry, and sandy environment. In 

 South Africa they are singularly lacking, owing to the inability 

 of the old luxuriant type of the Cretaceous to produce a local 

 secondary and xerophytic type of aggressive nature as it had 

 in Australia. Similarly for the case of South America. The 

 New Zealand myrtle members, outside of the tribe Myrteas, 

 and possibly of the subtribe ]\Ietrosiderese, appear to have been 

 derived from Australia, or from Australian and Malayasian 

 waifs. It is quite conceivable that the Metrosiderea? may have 

 developed in the north and entered the New Zealand during 

 its connection with Australia by way of New Guinea or North 

 Queensland. 



The Myrtese, like their allies, the Combretacea?, Melasto- 

 macese, and Rhizophoraeese, are essentially lovers of shelter, 

 moisture, and heat, and were specially unfitted, as were also 

 the Myrteae proper, to withstand the great cold of the Glacial 

 Period in Eurasia and North America. 



(4) Rutacece. 



The Rutaeese are essentially magnificent and luxuriant 

 arborescent forms, which as the genera Xanthoxylum and allied 

 forms, are widespread over the fertile tropics as primary types, 



