RELATIONSHIP OF AUSTRALIAN TERRESTRIAL FORMATIONS. 311 



Ideal Distribution of Genera from independent or vndely- 

 separated geograjyhical centres. 



On the hypotheses that all organic genera did not arise and 

 radiate repeatedly from one geographical centre only, and that a 

 considerable space of time would be consumed in the greater 

 extremes of distribution as regards terrestrial plants of higher 

 organisation, a diagram has been designed,* roughly to illustrate 

 the possible complication and inversion of order arising out of 

 the radiating distribution of genera from widely-separated centres ; 

 and also illustrating the different nature of the possible associates 

 to be met with at ditierent stations sliould the survivals succeed 

 in reacliing a middle station or the antipodes of the place of their 

 genei'ic origin. 



The cross dotted lines indicate tlie possible lapse of geological 

 time between the commencement and close of the migration of 

 each genus, and also the curious interweaving of different genera 

 which originated in centres widely apart. 



•Papers and Proc. R. Soc. Tas, 18S6, p. 182 (to face). 



