Tropical Character of the New Zealand Flora Explained.—In this origin of the New Zealand fauna by a north-western route from North-eastern Australia, we find also an explanation of the remarkable number of tropical groups of plants found there: for though, as Sir Joseph Hooker has

shown, a moist and uniform climate favours the extension of tropical forms in the temperate zone, yet some means must be afforded them for reaching a temperate island. On carefully going through the Handbook, and comparing its indications with those of Bentham's Flora Australiensis, I find that there are in New Zealand thirty-eight thoroughly tropical genera, thirty-three of which are found in Australia—mostly in the tropical portion of it, though a few are temperate, and these may have reached it through New Zealand[[187]]. To these we must add thirty-two more genera, which, though chiefly developed in temperate Australia, extend into the tropical or sub-tropical portions of it, and may well have reached New Zealand by the same route.

On the other hand we find but few New Zealand genera certainly derived from Australia which are especially temperate, and it may be as well to give a list of such as

do occur with a few remarks. They are sixteen in number, as follows:—

1. Pennantia (1 sp.). This genus has a species in Norfolk Island, indicating perhaps its former extension to the north-west.

2. Pomaderris (3 sp.). One species inhabits Victoria and New Zealand, indicating recent trans-oceanic migration.

3. Quintinia (2 sp.). This genus has winged seeds facilitating migration.

4. Olearia (20 sp.). Seeds with pappus.

5. Craspedia (2 sp.). Seeds with pappus. Alpine; identical with Australian species, and therefore of comparatively recent introduction.

6. Celmisia (25 sp.). Seeds with pappus. Only three Australian species, two of which are identical with New Zealand forms, probably therefore derived from New Zealand.

7. Ozothamnus (5 sp.). Seeds with pappus.

8. Epacris (4 sp.). Minute seeds. Some species are sub-tropical, and they are all found in the northern (warmer) island of New Zealand.

9. Archeria (2 sp.). Minute seeds. A species common to E. Australia and New Zealand.

10. Logania (3 sp.). Small seeds. Alpine plants.

11. Hedycarya (1 sp.).

12. Chiloglottis (1 sp.). Minute seeds. In Auckland Islands; alpine in Australia.

13. Prasophyllum (1 sp.). Minute seeds. Identical with Australian species, indicating recent transmission.

14. Orthoceras (1 sp.). Minute seeds. Identical with an Australian species.

15. Alepyrum (1 sp.). Alpine, moss-like. An Antarctic type.

16. Dichelachne (3 sp.). Identical with Australian species. An awned grass.

We thus see that there are special features in most of these plants that would facilitate transmission across the sea between temperate Australia and New Zealand, or to both from some Antarctic island; and the fact that in several of them the species are absolutely identical shows that such transmission has occurred in geologically recent times.

Species Common to New Zealand and Australia Mostly Temperate Forms.—Let us now take the species which are common to New Zealand and Australia, but found nowhere else, and which must therefore have passed from one country to the other at a more recent period than the mass of genera with which we have hitherto been dealing. These are ninety-six in number, and they present a striking contrast to the similarly restricted genera in being wholly temperate in character, the entire list presenting only a

single species which is confined to sub-tropical East Australia—a grass (Apera arundinacea) only found in a few localities on the New Zealand coast.

Now it is clear that the larger portion, if not the whole, of these plants must have reached New Zealand from Australia (or in a few cases Australia from New Zealand), by transmission across the sea, because we know there has been no actual land connection during the Tertiary period, as proved by the absence of all the Australian mammalia, and almost all the most characteristic Australian birds, insects, and plants. The form of the sea-bed shows that the distance could not have been less than 600 miles, even during the greatest extension of Southern New Zealand and Tasmania; and we have no reason to suppose it to have been less, because in other cases an equally abundant flora of identical species has reached islands at a still greater distance—notably in the case of the Azores and Bermuda. The character of the plants is also just what we should expect: for about two-thirds of them belong to genera of world-wide range in the temperate zones, such as Ranunculus, Drosera, Epilobium, Gnaphalium, Senecio, Convolvulus, Atriplex, Luzula, and many sedges and grasses, whose exceptionally wide distribution shows that they possess exceptional powers of dispersal and vigour of constitution, enabling them not only to reach distant countries, but also to establish themselves there. Another set of plants belong to especially Antarctic or south temperate groups, such as Colobanthus, Acæna, Gaultheria, Pernettya, and Muhlenbeckia, and these may in some cases have reached both Australia and New Zealand from some now submerged Antarctic island. Again, about one-fourth of the whole are alpine plants, and these possess two advantages as colonisers. Their lofty stations place them in the best position to have their seeds carried away by winds; and they would in this case reach a country which, having derived the earlier portion of its flora from the side of the tropics, would be likely to have its higher mountains and favourable alpine stations to a great extent unoccupied, or occupied by plants unable to compete with specially adapted alpine groups.