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



of extratropical Australia and South Africa offered a home to 

 these trees, and, thus, during the long gradual differentiation 

 of the climate, the trees became smaller, and they developed 

 marked xerophilous characters; and in proportion as the types 

 became specialized and reduced in size or dwarfed, so did such 

 types become vigorous and aggressive as Grevillea, Hakea, 

 Petrophila, Isopogon, and Persoonia. 



(3) Composites. 



The problem of the development of the Composite as also 

 of the Ericaceae, Epacridaceee, Campanulacea?, Lobeliaceae and 

 allied types, might be considered equally well under the heading 

 "The South African Problem" or the "Northern-Hemisphere 

 Problem." 



In South Africa and Australia the following genera are 

 common : 



Australian 



Species. 



South African Species. 



Senecio 



30 



200 



Gnaplialium 



7 



8 to 10 



Helichrysum 



70 



140 to 150 



Helipterum 



53 



12 



Cassinia 



13 



1 



Athrixia 



7 



6 



Cotula 



8 



22 



Of these Senecio and Gnaplialium are cosmopolitan, Heli- 

 chrysum has 26 species in Tropical Africa, 40 species in Mada- 

 gascar, and the genus also extends into Worth Africa, Europe 

 and Central Asia. Helipterum may be considered as a sub- 

 genus of Helichrysum for the purpose of distribution. Cas- 

 sinia may be discarded as doubtful or as a waif, while Cotula 

 has also six species in Europe and Asia. As against this 

 resemblance with Helichrysum, Helipterum and Athrixia, the 

 absence from Australia of the whole of the two South African 

 tribes, Calendulaceae and Arctotidese, may be cited. 



It would perhaps be advisable to preface the accompanying 

 brief notes of the probable origin of the Compositse in Australia 

 and South Africa, by mentioning the distribution of the asters, 

 the daisies, and the groundsels, as set out by Bentham in his 

 monograph on the Compositae. 



Aster in the broader sense comprises the true asters of the 

 northern hemisphere and a few genera almost inseparable from 

 it except in habit which occur in the southern hemisphere and 

 in Hawaii. 



