wever, been obtained since
the appearance of Sir Joseph Hooker's works, and I therefore determined to
apply to them the same method of discussion and treatment which has been
usually successful with similar problems in the case of animals. The fact
above noted, that New Zealand was connected with Australia in its northern
and tropical portion only, of itself affords a clue to one portion of the
specialities of the New Zealand flora--the presence of an unusual number of
tropical families and genera, while the temperate forms consist mainly of
species either identical with those found in Australia or closely allied to
them. But a still more important clue is obtained in the geological
structure of Australia itself, which is shown to have been for long periods
divided into an eastern and a western island, in the latter of which the
highly peculiar flora of temperate Australia was developed. This is found
to explain with great exactness the remarkable absence from New Zealand of
all the most abundant and characteristic Australian genera, both of plants
and of animals, since these existed at that time only in the _western_
island, while New Zealand was in connection with the _eastern_ island alone
and with the tropical portion of it. From these geological and physical
facts, and the known powers of dispersal of plants, all the main features,
and many of the detailed peculiarities of the New Zealand flora are shown
necessarily to result.

Our last chapter is devoted to a wider, and if possible more interesting
subject--the origin of the European element in the floras of New Zealand
and Australia, and also in those of South America and South Africa. This is
so especially a botanical question, that it was with some diffidence I
entered upon it, yet it arose so naturally from the study of the New
Zealand and Australian floras, and seemed to have so much light thrown upon
it by our preliminary studies as to changes of climate and the causes which
have favoured the distribution of plants, that I felt my work would be
incomplete without a consideration of {544} it. The subject will be so
fresh in the reader's mind that a complete summary of it is unnecessary. I
venture to think, however, that I have shown, not only the several routes
by which the northern plants have reached the various southern lands, but
have pointed out the special aids to their migration, and the motive power
which has urged them on.

In this discussion, if now