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Show 474 ISLAND LIFE. [PART. II. anC! abundant see d s must b e d1. sperse d by the wind almost as readily as the spores of ferns. . . Another specialised group-the Scrophulan?ere, abounds m N ew Zealand , where there are sixty-two species; bu. t thongh almost all the genera are Australian only three speCies are so. Here, too, the seeds are usually very small, and the powers of dispersal great, as shown by sever~! Europea~ genera- Veronica, E1.&ph?YMia, and Lirnosella, bemg found m the southern heniisphere. Looking at the whole series of these Australo-New Zealand plants, we find the most highl~ specialised group~-Co:npos~tre, Scrophularinere, Orchidere-w1th a small proportiOn of IdentiCal species (one-thirteenth to one-twentieth), the less highly specialised- Ranunculacere, Onagrarire and Ericere-with a higher proportion (one-ninth to one-sixth), and the least sp8cialisedJuncere, Cyperacere and Graminere-with the high proportion in each case of one-fourth. These nine are the most important New Zealand orders which contain species common to that country and Australia and confined to them ; and the marked correspondence they show between high specialisation and want of specific identity, while the generic identity is in all cases approximately equal, points to the conclusion that the means of diffusion are, in almost all plants ample, when long periods of time are concerned, and that diversities in this respect are not so important in determining the peculiar character of a derived flora, as adaptability to varied conditions, great powers of multiplication, and inherent vigour of constitution. This point will have to be more fully discussed in treating of the origin of the Antarctic and north temperate members of the New Zealand flora. Summa1:; a,nd Conclusion on the New Zealand Fl01·a.-Confining ourselves strictly to the direct relations between the plants of New Zealand and of Australia, as I have done in the preceding discussion, I think I may claim to have shown, that the union between the two countries in the latter part of the Secondary epoch at a time when Eastern Australia was widely separated from Western Australia (as shown by its geological formation and by the contour of the sea-bottom) does sufficiently account CHAP. XXIT .] THE FLOHA OF NEW ZEALAND. 475 for all the main features of the New Zealand flora. It shows why the basis of the flora is fundamentally Australian both as regards orders and genera, for it was due to a direct land connection between the two countries. It shows also why the great mass of typical Australian forms are unrepresented, for the Australian flora is typically wcsteTn and temperate, and New Zealand received its immigrants from the eastern island which had itself received only a fragment of this flora, and from the t1·opical end of this island, and thus could only receive such forms as were not exclusively temperate in character. It shows, further, why New Zealand contains such a very large proportion of tropical forms, for we see that it derived the main portion of its flora directly from the tropics. Again, this hypothesis shows us why, though the specially Australian genera in New Zealand are largely tropical or sub-tropical, the specially Australian species are wholly temperate or alpine; for these are comparatively recent arrivals, they must have migrated across the sea in the temperate zone, and these temperate and alpine forms are exactly such as would be best able to establish themselves in a country already stocked mainly by tropical forms and their modified descendants. This hypothesis further fulfils the conditions implied in Sir Joseph Hooker's anticipation that -"these great differences (of the floras) will present the least difficulties to whatever theory may explain the whole case,"for it shows that these differences are directly due to the history and development of the Australian flora itself, while the resemblances depend upon the most certain cause of all such broad resemblances-actual land connection. One objection will undoubtedly be made to the above theory, -that it does not explain why some species of the prominent Australian genera AcaC?:a, Eucalypt~ts, Melaleuca, Grevillea, &c., have not reached New Zealand in recent times along with the other temperate forms that .have established themselves. But it is doubtful whether any detailed explanation of such a negative fact is possible, while general explanations sufficient to cover it are not wanting. Nothing is more certain tban that numerous plants never run wild and establish themselves in .countries where they nevertheless grow freely if cultivated |
