1899] ORIGIN OF AUSTRALIAN FLORA 201 



our command. Is it so certain that all the species of the Scandinavian 

 flora have originated in the northern hemisphere ? Sir Joseph Hooker, 

 it is true, guards himself verbally from this assumption by enumerating 

 certain genera found south as well as north of the tropics as " emi- 

 nently characteristic " of the northern flora. But the inference remains 

 nevertheless, and we have only to consider the case of the Marsupials 

 and Monotremes — orders " eminently characteristic " of Australia, but 

 which we know upon zoological evidence not to have originated there — 

 we have only to consider this case to see how unjustified is the inference, 

 and how liable we may be, by adopting it, to fall into complete error. 

 And it will be well here to deal, by way of example, with a few genera 

 usually regarded as of northern origin, but which, it is maintained, 

 may have originated in the southern hemisphere. There is Senecio, 

 for instance, a genus strongly represented in extra-tropical South 

 America (Philippi enumerates no less than 117 species as members 

 of the Chilian flora alone) and in South Africa, and less strongly in 

 Australia and New Zealand. The general view about such a case as 

 this is that the areas just mentioned are isolated from each other, 

 while each is in complete or almost complete connection with the 

 great northern continent ; hence the probability is that they were 

 stocked from the latter. But, given a means whereby the species of 

 Senecio could pass from north to south, there is no inherent reason 

 why they might not have migrated in the opposite direction, say, for 

 example, from South Africa by way of Eastern Asia into America on 

 the one hand, and via what is now the Indian Archipelago into 

 Australia on the other, and certain affinities between the floras of 

 South Africa and Australia seem to show that some such migration 

 has actually occurred. Again, take Drosera, a genus which, from the 

 bias of early association, is usually regarded as having originated in the 

 northern hemisphere, but which, in point of numbers and of differentia- 

 tion, is far better represented south of the Equator than north of it, and 

 very strongly in Australia itself. Then there is Veronica, with 

 15 Australian and no less than 40 New Zealand species, with 18 

 species in India, chiefly the Himalayas, about 20 species in North 

 America, and not quite so many in China. Out of a total of some 

 160 species for the whole world rather more than one-third are 

 natives of Australia or New Zealand or both. Aster, too, is a case in 

 point, for though the Australian Olearia and the South African Felicia 

 have been separated from it, and may still be kept up for convenience 

 sake, in no essential respect do they differ from Aster, of which over 

 200 species are North American, while there are about 50 species of 

 Felicia and nearly 70 species of Olearia in Australia and 20 in New 

 Zealand. Now Aster is a genus eminently characteristic of the nearctic 

 portion of the great northern land-mass, but if it had a northern origin, 

 why is it so rare in Europe, a region where many of its species have 

 become naturalised and are able to maintain themselves ? Why may 



