ian genera, and even species, reappear everywhere from Lapland and
Iceland to the tops of the Tasmanian Alps, in rapidly diminishing numbers
it is true, but in vigorous development throughout. They abound on the Alps
and Pyrenees, pass on to the Caucasus and Himalayas, thence they extend
along the Khasia Mountains, and those of the peninsulas of India to those
of Ceylon and the Malayan Archipelago (Java and Borneo), and after a hiatus
of 30deg they appear on the Alps of New South Wales, Victoria, and
Tasmania, and beyond these again on those of New Zealand and the Antarctic
Islands, many of the species remaining unchanged throughout! It matters not
what the vegetation of the bases and flanks of these mountains may be; the
northern species may be {511} associated with alpine forms of Germanic,
Siberian, Oriental, Chinese, American, Malayan, and finally Australian, and
Antarctic types; but whereas these are all, more or less, local
assemblages, the Scandinavian asserts his prerogative of ubiquity from
Britain to beyond its antipodes."[137]

It is impossible to place the main facts more forcibly before the reader
than in the above striking passage. It shows clearly that this portion of
the New Zealand flora is due to wide-spread causes which have acted with
even greater effect in other south temperate lands, and that in order to
explain its origin we must grapple with the entire problem of the transfer
of the north temperate flora to the southern hemisphere. Taking, therefore,
the facts as given by Sir Joseph Hooker in the works already referred to, I
shall discuss the whole question broadly, and shall endeavour to point out
the general laws and subordinate causes that, in my opinion, have been at
work in bringing about the anomalous phenomena of distribution he has done
so much to make known and to elucidate.

_Aggressive Power of the Scandinavian Flora._--The first important fact
bearing upon this question is the wonderful aggressive and colonising power
of the Scandinavian flora, as shown by the way in which it establishes
itself in any temperate country to which it may gain access. About 150
species have thus established themselves in New Zealand, often taking
possession of large tracts of country; about the same number are found in
Australia, and nearly as many in the Atlantic states of America, where they
form the commonest weeds. Whether or not we accept Mr. Darwin's explanation
of this power as due to development in