322 PROCEEDINGS OF SECTION D. 



Another feature pointing in the same directions is the high 

 state of specific luxuriance in many of its genera, twenty of which 

 in the extra-tropical part of South A ustralia contain two hundred 

 and forty-one species, twelve to a genus, or more than one-fourth 

 of the flora. Nevertheless, for the whole flora the number of 

 species per genus is low, namely 2.7, and is actually the same for 

 the exotic as for the endemic genera. Thus three hundred and 

 ninety-six exotic genera contain five hundred and sixty species, 

 and one hundred and forty-four endemic genera contain two 

 hundred and seven species. 



A process of differentiation seems to be in progress because of 

 the local i^acial cliaracters exhibited in some genera and species. 



Of the latter of these may be mentioned as noteworthy : — 



Arhutilon oxycarpum, var. malvfu/olium. 



Salsola kali, var. strobolifera. 



Crotalaria dissitiflora, var. eremcea. 



Daricinia micropetala, var. cicatricosa. • 



Cassia circinita, var. glaucescens. 



Panicum divaricatissimum, var. amnophilum. 



Panicum jMuciflorum, var. fastigiatum. 



Panicum Mitchelli, var. 



Eriachne ovata, var. 



Further, the many monotypic genera which are for the most 

 part offsets of Australian types, altered by new surroundings, 

 show no singularity which may be attributed to a high antiquity. 



An indispensable property of the Eremian plants is that of 

 rapid germination so as to take advantage of tlie rare opportu- 

 nities when the physical and hygrometric conditions of the soil 

 are favourable, and quite irrespective of temperature. Moreover, 

 the long periods of droughts intervening bftween the favourable 

 periods necessitates another quality in their seeds, that of resist- 

 ance to long exposure. The protection necessary to ensure a long 

 suspended vitality reacts adversely by increasing the difficulty of 

 rapid germination ; but in extreme cases at least, this seems to be 

 met by the fruit and seed eatiug propensities of certain animals. 

 In this connection, we may have an explanation of the wide 

 dispersal of some species of plants by the agency of migratory 

 animals. 



Individual tenacity of life is another essential condition of 

 maintaining a foothold in the Eremian Region. To one who has 

 seen this country for the first time during a severe drought will 

 wonder that the shrubby growth, reduced to a mass of dry twigs 

 and withered leaves can by any possibility recover, but on the first 

 copious rains the transformation is marvellous. Now and again 

 a few agral weeds reach the outskirts of the Eremain Region, but 

 they have not succeeded in permanently establishing themselves. 



The Autochthonian flora, after elimination of the emigrant 

 species of exotic origin, consists of species belonging, for the most 

 part, to genera endemic in Australia, whilst, on the other hand, 



