Fauna and Flora of New Zealand. 439 
more reasonable to suppose that some of the tropical species 
have died out in Australia than that all the 16 genera have 
crossed the sea, an opinion not shared in by Sir J. Hooker, 
or by Mr. T. Kirk*. 
Passing on now to the probably antarctic genera, that is 
southern genera which have spread east and west in south- 
temperate latitudes, we find that they number 20, containing 
76 species, of which only 60 per cent. are endemic. Nineteen 
of the species are also found in Australia or T’asmania, and 
11 or 12 in South America. There are also 56 genera of 
north-temperate plants, which probably spread with the 
antarctic forms, containing 199 species, of which 67 per 
cent. are peculiar to New Zealand. ‘The remaining 87 
genera I am unable to place. Most of them belong to two 
or more geographical elements, but others—such as Fagus 
—are doubtful. 
Statistical results like these are always open to the objection 
that the data on which they rest are incomplete and more or 
less erroneous (for example, Corzaria and Gunnera may 
belong to the antarctic element, and Drosera to the South- 
American). They also assume that the rate of variation is 
equable, which of course cannot be strictly accurate. But 
this method of investigation has been used with great success 
in geology, and it can, I think, be trusted here for establishing 
the two following conclusions:—First, that the northern 
immigration, taken as a whole, was anterior to the southern 
immigration, also taken as a whole; and second, that the im- 
migration of the subtropical South-American genera belongs 
to the first period and not to the last. The first conclusion is 
similar to that of Mr. Wallace, but arrived at in a different 
way. ‘The second is opposed to Mr. Wallace’s idea that the 
South-American plants passed through New Zealand and 
antarctic lands during a warm Miocene period, which is also 
opposed by the fact that a number of Australian genera are 
found in South America but not in New Zealand. The fact 
that very few of our South-American genera are absent from 
Australia, while a large number of our Australian genera are 
absent from South America, makes it probable that there have 
been at least two migrations into New Zealand from the 
north, and that the South-American element belongs to the 
first of these only. This is borne out by the distribution of 
* See Trans. N. Z. Institute, vol. xi. p. 546. 
+ Itake the following as typical :—Colobanthus, Oxalis, Acena, Donatia, 
Tillea, Drosera, Apium, Nertera, Abrotanella, Cotula, Forstera, Pernet- 
tya, Ourisia, Drapetes, Callixene, Rostkovia, Gaimardia, Carpha, Oreobolus, 
and Uneimia. 
