DIFFERENTIATION 



317 



The Australian Flora. — To illustrate the argument reference 

 may be made to the Australian flora, where we find world-ranging 

 families with a special Australian impress, such as the Leguminosce 

 and the Proteacece, associated with families of later development and 

 of purely Australian origin which represent, as in the Goodeniacece, a 

 regional modification of a primitive widely distributed family type, 

 the modification of which has been so extensive that the connections 

 with the other descendants of the same family type in other parts 

 of the world have been lost in the differentiation process. After I 

 had elaborated this argument in some detail for this chapter I found 

 that the whole matter had been treated on similar lines, but on a far 

 more extensive scale, by Mr. E. C. Andrews. Working in Australia, 

 with abundant material at his disposal and with the willing aid of 

 some of the foremost of Australian botanists, he has endeavoured to 

 co-ordinate the evolution of the Australian flora with the develop- 

 ment of the physical conditions, and it is with his papers on this 

 subject that I will now deal. 



Mr. Andrews had for years devoted himself as a geologist to 

 unravelling the history of Australia as a land-mass, and he found in 

 the development of the present land-forms and in the conditions in 

 which they were produced a key to the various stages in the building 

 up of the island continent. Whilst thus engaged, his attention was 

 drawn to a remarkable relation existing in New South Wales between 

 the arrangement of the purely Australian and extra-Australian 

 plants and the physical, geological and climatic features of the region. 

 This led him to reflect on the manner in which the Australian flora 

 as a whole had responded to the different stages in the development 

 of the continent, and he was induced to look to the Myrtacece and 

 Leguminosce as orders especially well fitted for the investigation of 

 this subject. 



In December 1913 his paper on " The Development of the Natural 

 Order Myrtacese" was issued in the Proceedings of the Linnean 

 Society of New South Wales. For him in this paper the predominant 

 influence in plant- evolution has been neither Time, nor Heredity, 

 nor Variation, nor Selection, but geographical environment. The 

 evolution of floras represents the response of plant-life to variations 

 in climatic and soil conditions during ages of changing geographical 

 surroundings. Taking the position that cosmopolitan and genial 

 climates at different geological periods tended to produce cosmopoli- 

 tan or widely ranging floras, whilst variation in climate in the past 

 tended to produce differentiated and localised floras, he applies this 

 view to the differentiation of the Myrtacece from deduced generalised 

 primitive forms of the Cretaceous age. It is argued that at this 

 period the family, responding to the relatively uniform conditions of 

 a mild and moist climate that prevailed over much of the globe, had 

 a much wider range than it now has, and that it then covered the 

 tropics as well as a large part of the present temperate regions. 



The manner in which the primitive types differentiated in response 

 to the differentiation of climatic and other conditions since the late 

 Mesozoic is then indicated. The early types would become more 

 and more restricted to the regions that preserved their original 



