XXIV FLORA OF NEW ZEALAND,
retii’emcnt of the plants to the summit of the New Zealand mountains*, would be tbe necessaiy
consequence of the amelioration of climate th a t followed the isolation of New Zealand, and the
replacement of the Antarctic continent by the present ocean.
The climate tlu’oughout the south temperate zone is so equable, and tbe isothermal lines ai’c so
parallel to those of latitude, th a t it is not easy for the New Zealand natui-ahst to realize the altered
circumstances th a t would render tlie plains of his island suitable for the growth of plants th a t now
inhabit its mountains o n ly t; but if be 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 la titu d e ; tha t London, with
a mean tcmperatm’e 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 tbe destruction of all tlie native plants th a t did not retire to its mountain-tops, and
favouring the immigration of the species of a more genial climate.
The fii'st inference fr*om such an hypothesis is th a t 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 he classed under three heads j : :—
1. Those th a t contain identical or representative species of the Antarctic Flora, and none that
are peculiarly A rc tic ; as the Tasmanian and New Zealand Alps§.
2. Those th a t contain, besides these, peculiarities of the Northern aud Arctic Floras | | ; as the
South American Alps.
3. Those th a t contain the peculiarities of neither; as the rhountains of South Africa and the
Pacific Islands.
* With regard to the British moiratains, 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 ice
transport being an active agent in dispersion. A lowering of 10° of mean temperature would render tbe 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 hays 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 tbe level of the sea in South Chili, at the
latitude of Dusky Bay; and if they have done so in the latter locality, they will have 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 pecuUarly 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 he 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 Acxna, Brapeles, Bonatia, Gunnera, Oreomyr-
rhis, Lagenophora, Foi'stera, Ourisia, Fagus, Callixene, Astelia, Gaimardia, Alepyrim, Oreoholus, Carpha, Uncinia.
II Berberis, Sisymbrium, Thlaspi, Arahis, Braha, Sayina, Lychnis, Cerasiium, Fragaria, Laihyrus, Vicia, Hip-
puris, Chrysosplenium, Ribes, Saxifraga, Valenana, Aster, Ilieracium, Stachys, Primula, Anagallis, Pinyuicula,
Staiice, Empeirum, Phleum, Elymus, Hordeum.
AYc tlius observe th a t the want of an Ai’ctic or Antarctic Flora at all in the Pacific islands,
and the presence of an Arctic one in the American Alps, arc the prominent features; and I shall
confine my remarks upon these to the fact that, with regard to the isolated islands of the Pacific,
they arc situated in too warm a latitude to have had their temperature cooled by changes in the re la tive
position of land and ocean, so as to have harboured an Antarctic vegetation. AA’ith regard to the
South American Alps, there is direct land communication along the Andes from Arctic to Antarctic
regions; by which not only may the strictly Arctic genera and species have migrated to Cape Horn,
but by which many Antarctic ones may have advanced northward to th e equator*.
There is still another point in connection with the subject of the relative antiquity of plants, and
in adducing it I must again refer to tbe ‘ Principles of Geology,’ where it is said, “ As a general rule,
species common to many distant provinces, or those noiv found to inhabit many distant parts of the
globe, are to be regarded as the most ancient . . . . the ir wide diffusion shows th a t they have
had a long time to spread themselves, and have been able to surrive many important changes in
Physical Geography t . ’’ I f this be true, it follows th a t, consistently with th e theory of the antiquity
of the Alpine flora of N ew Zealand, we should find amongst the plants common to New Zealand and
the Antarctic islauds, some of the most cosmopolitan; and we do so in Montia fontana, Callitriche
verna, Cardamine hirsuta, Epilobium tetragonum, and many others.
Ou the other hand, it must be recollected th a t there are other causes besides antiquity and
facility for migration, th a t determine the distribution of plants; these are tlieir power, mentioned
above, of invading and effecting a settlement in a country preoccupied with its own species, and their
adaptability to various climates; r i t h regard to the first of these points, it is of more importance
than is generally assumed, and I have alluded to its effects under Sonchus, in the body of this work.
As regards climates, the plants mentioned above seem wonderfully indifferent to its effects J.
Again, even thougb w’e may safely pronounce most species of ubiquitous plants to have outlived
many geological changes, we may not reverse tbe position, aud assume local species to be amongst the
most recently created; for whether (as has been conjectured) species, like individuals, die out in the
course of time, following some inscrutable law whose operations we have not yet traced, or whether
(as in some instances Ave know to be tbe case) they are destroyed by natural causes (geological or
others), they must in either case become scarce and local Avhile they are in process of disappearance.
In the above speculative review of some of the causes which appear to affect the life and range
of species in the vegetable kingdom, I have not touched upon one point, namely, th a t wliicli concerns
the original introduction of existing species of plants upon the earth. I have assumed th a t they have
existed for ages in the forms they uoav retain, th a t assumption agreeing, in my opinion, Avith the facts
elicited by a surA'ey of aU the phenomena they present, and, according to the most eminent zoolo-
* AVhy these Antarctic forms have not extended into North America, as the Arctic ones have into South America,
IS a curious problem, aud the only hypothesis that suggests itself is derived from the fact that though the Panama
Andes are not uoav sufficiently lofty for the transit of either, there is nothing to contradict the supposition that they
may have had sufficient altitude at a former period, and that one which preceded the advance of the Antarctic species
to so liigh a northern latitude.
t Principles of Geology, cd. 9. p. 702.
X Mr. Watson (Cybelc Britannica) gives the range of Callitriche in Britain alone as including mean temperatures
of 40° to 52°, and as ascending from the level of the sea to nearly 2000 feet in the East Highlands of
Scotland. Montia, according to the same authority, enjoys a range of 36° to 52°, and ascends to 3300 feet; Epilo-
bium, a temperature of 40° to 51°, and ascends to 2000 feet; Cardamine, a temperature of 37° to 52°, and ascends
to 3000 feet.
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