INTRODUCTORY ESSAY. Xix 
British Museum. When re-found in New Zealand it was described as new, and called O. cataracte, 
and when found a third time in Tasmania, was called by still a third name, O. lactea. In this case 
a more important fact was smothered than that of the distribution of O. corniculata, namely, that of 
a very peculiar plant of the south temperate zone being common to these three widely sundered 
localities. 
Many similar instances might be added, for there are several New Zealand plants (as Pteris 
aguilina) that have a different name in almost every country in the world,’ and, partly from 
changes in nomenclature, partly from the reduction of species, I have found myself obliged to quote 
1500 names for the 720 New Zealand flowering-plants described, and 1 believe I might have doubled 
the number had my limits not obliged me to reduce the synonymy as much as possible; in many 
cases too much, I fear, for the requirements of working botanists in Europe. 
$ 4. 
- The distribution of species has been effected by natural causes, but these are not necessarily the 
same as those to which they are now exposed. 
* Of all the branches of Botany there is none whose elucidation demands so much preparatory study, 
or so extensive an acquaintance with plants and their affinities, as that of their geographical distribu- 
tion. Nothing is easier than to explain away all obscure phenomena of dispersion by several specu- 
lations on the origin of species, so plausible that the superficial naturalist may accept any of them; 
and to test their soundness demands a comprehensive knowledge of facts, which moreover run great 
risk of distortion in the hands of those who do not know the value of the evidence they afford. I 
have endeavoured to enumerate the principal facts that appear to militate against the probability of 
the same species having originated in more places (or centres) than one; but in so doing I have only 
partially met the strongest argument of all in favour of a plurality of centres, viz. the difficulty of 
otherwise accounting for the presence in two widely sundered localities of rare local species, whose 
seeds cannot have been transported from one to the other by natural causes now in operation. To take 
an instance: how does it happen that Edwardsia grandiflora inhabits both New Zealand and South 
America? or Ozalis Magellanica both these localities and Tasmania? The idea of transportation by 
aerial or oceanic currents cannot be entertained, as the seeds of neither could stand exposure to the 
salt water, and they are too heavy to be borne in the air. Were these the only plants common to 
these widely-sundered localities, the possibility of some exceptional mode of transport might be ad- 
mitted by those disinclined to receive the doctrine of double centres; but the elucidation of the New 
Zealand Flora has brought up many similar instances equally difficult to account for, and has deve- 
loped innumerable collateral phenomena of equal importance, though not of so evident appreciation. 
These, which all bear upon the same point, may be arranged as follows :— 
1. Seventy-seven plants are common to the three great south temperate masses of land, Tas- 
mania, New Zealand, and South America. 
2. Comparatively few of these are universally distributed species, the greater part being peculiar 
to the south temperate zone. 
3. There are upwards of 100 genera, subgenera, or other well-marked groups of plants entirely 
or nearly confined to New Zealand, Australia, and extra-tropical South America. These are repre- 
sented by one or more species in two or more of these countries, and they thus effect a botanical rela- 
tionship or affinity between them all, which every botanist appreciates. 
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