Asiatic genera of which we find no trace in
New Zealand or South America, or any other Antarctic land. We find, in
fact, in Australia two distinct sets of European plants. First we have a
number of species identical with those of Northern Europe or Asia (of the
most characteristic of which--thirty-eight in number--Sir Joseph Hooker
gives a list); and in the second place a series of European genera usually
of a somewhat more southern character, mostly represented by very distinct
species, and all absent from New Zealand; such as Clematis, Papaver,
Cleome, Polygala, Lavatera, Ajuga, &c. Now of the first set--the North
European _species_--about three-fourths occur in some parts of America,
{524} and about half in South Temperate America or New Zealand; whence we
may conclude that most of these, as well as some others, have reached
Australia by the route already indicated. The second set of
Australo-European genera, however, and many others characteristic of the
South European or the Himalayan flora, have probably reached Australia by
way of the mountains of Southern Asia, Borneo, the Moluccas, and New
Guinea, at a somewhat remote period when loftier ranges and some
intermediate peaks may have existed, sufficient to carry on the migration
by the aid of the alternate climatal changes which are known to have
occurred. The long belt of Secondary and Palaeozoic formations in East
Australia from Tasmania to Cape York continued by the lofty ranges of New
Guinea, indicates the route of this immigration, and sufficiently explains
how it is that these northern types are almost wholly confined to this part
of the Australian continent. Some of the earlier immigrants of this class
no doubt passed over to New Zealand and now form a portion of the peculiar
genera confined to these two countries; but most of them are of later date,
and have thus remained in Australia only.

_Proofs of Migration by way of the African Highlands._--It is owing to this
twofold current of vegetation flowing into Australia by widely different
routes that we have in this distant land a better representation of the
European flora, both as regards species and genera, than in any other part
of the southern hemisphere; and, so far as I can judge of the facts, there
is no general phenomenon--that is, nothing in the distribution of genera
and other groups of plants as opposed to cases of individual species--that
is not fairly accounted for by such an origin. It further