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 stronely 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 
