chap, xxii.] - THE FLORA OF NEW ZEALAND. 
473 
This last consideration throws light on a very curious point, 
which has been noted as a difficulty by Sir Joseph Hooker, that 
plants which have most clear and decided powers of dispersal 
by wind or other means, have not generally the widest specific 
range ; and he instances the small number of Composita3 com- 
mon to New Zealand and Australia. But in all these cases it 
will, I think, be found that although the species have not a wide 
range the genera often have. In New Zealand, for instance, 
the Compositse are very abundant, there being no less than 148 
species, almost all belonging to Australian genera, yet only nine 
species, or less than one-sixteenth of the whole, are identical in 
the two countries. The explanation of this is not difficult. 
Owing to their great powers of dispersal, the Australian Com- 
positse reached New Zealand at a very remote epoch, and such 
as were adapted to the climate and the means of fertilisation 
established themselves ; but being highly specialised plants with 
great flexibility of organisation, they soon became modified in 
accordance with the new conditions, producing many special 
forms in different localities ; and these, spreading widely, soon 
took possession of all suitable stations. Henceforth immigrants 
from Australia had to compete with these indigenous and well- 
established plants, and only in a few cases were able to obtain 
a footing ; whence it arises that we have many Australian types, 
but few Australian species, in New Zealand, and both phenomena 
are directly traceable to the combination of great powers of dis- 
persal with a high degree of specialisation. Exactly the same 
thing occurs with the still more highly specialised Orchideae. 
These are not proportionally so numerous in New Zealand 
(thirty-eight species), and this is no doubt due to the fact that 
so many of them require insect-fertilisation often by a particular 
family or genus (whereas almost any insect will fertilise Com- 
positae), and insects of all orders are remarkably scarce in New 
Zealand. This would at once prevent the establishment of 
many of the orchids which may have reached the islands, while 
those which did find suitable fertilisers and other favourable 
conditions would soon become modified into new species. It is 
thus quite intelligible why only three species of orchids are 
identical in Australia and New Zealand, although their minute 
