CHAr. 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 disjDersal 

 by wind or other means, have Qioi generally the wildest specific 

 range ; and he instances the small number of Compositoe 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 Compositae 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- 

 positaB 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 OrchideEe. 

 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- 

 positse), and insects of all orders are remarkably scarce in New 

 Zealand. This w^ould 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 



