Dec, 



Iyl2 



] KEhLY, Concerning Acacia Phyllodest 119 



species ol the world arose. Its claim to this distinction is that 

 it is the only Australian acacia now common to the New 

 and Old Worlds, and is found more or less near to the habitats 

 of all acacias. All other species are endemic. The phyllodinous 

 type is peculiar to Australia and some adjacent islands. The 

 island species are not identifiable with Australian species, but 

 are near to tropical types. In Australia A. farnesiana is dis- 

 tributed over North Australia, Queensland, and the interior 

 of New South Wales, towards Cooper's Creek. It is thought 

 by some to be of American origin, and by other authorities as 

 indigenous to Africa, but it indeed appears to be so to Aus- 

 tralia. A. farnesiana is a much-branched shrub of considerable 

 size, and pinnate ; the stipules are converted into slender, 

 straight thorns, varying from J-inch long to minute, and some- 

 times to none. I am indebted to Bentham's " Flora Aus- 

 traliensis " for this information, and to Mueller's "Extra- 

 Tropical Plants" for the following extract: — "/I. farnesiana, 

 Dioscorides' small acacia. Indigenous to South Asia ; found 

 westward as far as Japan ; a native also of the warmer parts 

 of Australia as far south as the Darling River ; found spon- 

 taneously in tropical and sub-tropical America, but api)arently 

 not in tropical Africa. Professor Fraas has recognized in this 

 acacia the ancient plant." 



The original Australian habitat of A. farnesiana, though 

 tropical, was not arid. The deserts of Australia were at that 

 time probably seas, which subsequently receded. The climate, 

 inland at least — that is, between these sea-beds and the coast — 

 became more arid. Acacias growing there suffered season 

 after season from drought. The delicate feather-leaves fell 

 during years of suffering. Fresh shooting leaves necessary to 

 supply carbon dioxide from the air were too few to ])crform 

 the necessary functions. It was a struggle for existence — 

 the old struggle of the evolutionary theory. The plant fought 

 for food and breath, putting out little lateral processes on 

 branch and leaf-stalk, evidenced now by the decurrcnt ridges 

 and the flattened petiole. The plant survived, and extended 

 the process. The leaf-like one was found the best. Take 

 another stage in the history : The tree bore seed. The re- 

 sulting young i)lants bore first the little leaves of its forebears. 

 The environment was still the same, the struggle as great ; the 

 process was repeated. Similar struggles were going on in 

 different individuals widely sei)arated and in varying environ- 

 ments. Naturally, the results varied. Generation succeeded 

 generation ; seeds were transposed to many jxarts by the 

 different agencies — princi])ally by birds. Some may have been 

 carried back to an environment in which the i)innate leaf type 

 was ideal, and had remained normal. We now came face to 



