XXXIII SEED-DISPERSAL AND GEOLOGICAL TIME 505 



the nectar-feeding Drepanids are particularly partial ; and the 

 development of the extreme forms of these birds, as Mr. Perkins 

 observes in the Fauna Hawaiiensis, " is not comprehensible 

 without a knowledge of the island flora." Not only does he point 

 to the modifications in the form of the bill of the bird in connection 

 with the tubular form of the flowers ; but in at least one species of 

 these arborescent Lobeliaceae he shows that it is dependent on the 

 Drepanid for its fertilisation, and he inclines to the view that 

 changes such as that of lengthening of the bill may have taken 

 place side by side with the increasing length of the tubular flowers. 

 In connection with the Freycinetias of Hawaii, Mr. Perkins regards 

 the bill of the Ou, a, finch-like Drepanid of the genus Psittacirostra, 

 as " entirely formed and adapted for the purpose of picking out 

 the component parts " of the fruiting inflorescence. 



That in an isolated island-group birds and plants often 

 " differentiate " together is a fact well known in distribution. In 

 Hawaii, for instance, as I learn from Mr. Perkins, quite 45 per 

 cent, of the birds are peculiar ; whilst according to Dr. Hillebrand 

 80 per cent, of the flowering plants are confined to the group. 

 Then, again, in the Galapagos Islands, half of the plants and two- 

 thirds of the birds are confined to that archipelago. At the other 

 end of the series we have the Azores, with about a tenth of its 

 plants peculiar, and about 4 per cent, of its birds peculiar to the 

 islands, and Iceland with no endemic plants and, as far as I can 

 gather, few peculiar birds. 



Accepting Mr. Charles Dixon's view (TAe Migration of Birds, 

 1897) that specific differentiation does not occur along lines 

 of migration, we must assume that the differentiation of the 

 avifauna of an isolated group like Hawaii began with the 

 breaking off" of its regular communication through birds with 

 the outside world. I do not consider that in the past these 

 Pacific archipelagoes received their birds in any haphazard fashion, 

 as, for instance, in the guise of stragglers that had lost their way. 

 From the circumstance pointed out to me by Mr. Perkins that 25 

 of the 67 genera of Hawaiian birds are peculiar, we must postulate 

 a high antiquity for the bird fauna dating far back into the 

 Tertiary period. Mr. Perkins, who kindly supplied me with his 

 general views of the nature of the Hawaiian fauna, tells me that 

 it is '' positively oceanic-insular and could be continental only on the 

 supposition that everything continental had been at some time 

 destroyed and that the group had been subsequently re-stocked as 

 would any oceanic island." 



