CHAP. XXII THE FLORA OF NEW ZEALAND 503 



single species Avliicli is confined to sub-tropical East 

 Australia — a grass (AjJera arundinacca) 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 

 Kanunculus, Drosera, Epilobium, Gnaphalium, Senecio, 

 Convolvulus, Atriplex, Luzula, and many sedges and 

 grasses, whose exceptionally wide distribution shows that 

 they possess excei^tional 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 tem- 

 perate groups, such as Colobanthus, Acgena, 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. 



