xxiv FLORA OF NEW ZEALAND. 



retirement of the plants to the summit of the New Zealand mountains*, would be the necessary 

 consequence of the amelioration of climate that followed the isolation of New Zealand, and the 

 replacement of the Antarctic continent by the present ocean. 



The climate throughout the south temperate zone is so equable, and the isothermal lines are so 

 parallel to those of latitude, that it is not easy for the New Zealand naturalist to realize the altered 

 circumstances that would render the plains of his island suitable for the growth of plants that now 

 inhabit its mountains onlyt ; but if he glance at the map of the isothermal lines of the northern 

 hemisphere, he will see how varied are the climates of regions in the same latitude ; that London, with 

 a mean temperature of 51°, is in the same latitude as Hudson's Bay, where the mean temperature is 

 30°, and the soil ever frozen : and he will further be able to understand by a little reflection, how a 

 change in the relative positions of sea and land would, by isolating Labrador, raise its temperature 

 10°-15°, causing the destruction of all the native plants that did not retire to its mountain-tops, and 

 favouring the immigration of the species of a more genial climate. 



The first inference from such an hypothesis is that the Alpine plants of New Zealand, having 

 survived the greatest changes, are its most ancient colonists ; and it is a most important one in many 

 respects, but especially when considered with reference to the mountain floras of the Pacific and 

 southern hemisphere generally. These may be classed under three heads J : — 



1. Those that contain identical or representative species of the Antarctic Flora, and none that 

 are peculiarly Arctic; as the Tasmanian and New Zealand Alps§. 



2. Those that contain, besides these, peculiarities of the Northern and Arctic Floras || ; as the 

 South American Alps. 



3. Those that contain the peculiarities of neither; as the mountains of South Africa and the 

 Pacific Islands. 



* With regard to the British mountains, Professor Forbes imagines that they were islets in the glacial ocean, 

 and received their plants by transportation of seeds with soil, on ice from the Arctic regions. This appears to me 

 to want support, and there is much in the distribution of Arctic plants especially, wholly opposed to the idea of i«e 

 transport being an active agent iu dispersion. A lowering of 10° of mean temperature would render the greater 

 part of Britain suitable to the growth of Arctic plants ; it would give it the climate of Labrador, situated in the 

 same latitude on the opposite side of the Atlantic. Britain is the warmest spot in its latitude, and a very slight 

 geological change would lower its mean temperature many degrees. 



t The New Zealand naturalist has probably a very simple means of determining for himself whether his island 

 has been subject to a geologically recent amelioration of climate; to do which, let him examine the fiord-like bays of 

 the west coast of the Middle Island, for evidence of the glaciers which there exist in the mountains having formerly 

 descended lower than they now do. Glaciers to this day descend to the level of the sea in South Chili, at the 

 latitude of Dusky Bay ; and if they have done so in the latter locality, they wilPhave left memorials, in the shape of 

 boulders, moraines, and scratched and polished rocks. 



X I need scarcely remind my reader that in thus sketching the characteristics of these Alpine floras, I make 

 no allusion to exceptions that do not alter the main features. I am far from asserting that there are no peculiar 

 Arctic or Antarctic forms in the Pacific Islands, nor any peculiarly Arctic ones in Tasmania and New Zealand : but 

 if, on the one hand, future discoveries of such shall weaken the points of difference between these three mountain 

 regions, on the other they might be very much strengthened by adducing the number of Arctic species common 

 to the South American Alps, but not found in the others. 



§ These Antarctic forms are very numerous ; familiar ones are Acana, Drapeles, Donatio, Gunnera, Oreomyr- 

 rhis, Lagenophora, Forstera, O/irisia, Faff us, Callixene, Astelia, Gaimardia, Alepyrum, Oreobolus, Carpha, Urwinia. 



|| Berberis, Sisymbrium, Thlaspi, Arabia, Draba, Sagina, Lychnis, Cerastium, Fragaria, Lathyrus, Vicia, Hip- 

 pnris, Chrysosplenium, Mibes, Saxifraga, Valeriana, Aster, Eieracium, Stachys, Primula, Anagallis, Pinguecula, 

 Statice, Empdrum, Plileum, Flymus, Eordeum. 



