CHAPTER XXXIII 



SEED-DISPERSAL AND GEOLOGICAL TIME 



The shifting of the source of the Polynesian plants from the New to the Old 

 World. — The floral history of Polynesia stated in terms of geological time. — 

 The suspension of the agencies of dispersal in later periods. — Parallel 

 differentiation in the course of ages of climate, bird, and plant. — ■'New 

 Zealand. — Insects and bats as agents in plant-dispersal. — The effective 

 agency of sea-birds in other regions. — The observations of Ekstam. — The 

 Spitzbergen controversy. — The efficacy of ducks as distributors of aquatic 

 plants. — Summary. 



In the matter of the dispersal of seeds by birds in the tropical 

 Pacific, there are at least two questions which my readers must 

 have frequently put to themselves. The one would be concerned 

 with the shifting of the source of the Polynesian plants from 

 America to the Old World, which occurred probably near the 

 close of the Tertiary period. The other would be connected with 

 the suspension of the work of dispersal over a large portion of 

 Polynesia, which has become more and more pronounced as we 

 approach our own day. 



Stiggested Cause of the Shifting of the Source of the Polynesian 

 Plants from the New to the Old World. — In previous chapters we 

 have discussed the various epochs in the plant-stocking of these 

 islands. There was first the age of Coniferae, in which the islands 

 of the Western Pacific were only concerned, an age prior to the 

 appearance of the volcanic groups of the Tahitian and Hawaiian 

 regions, and placed in the Secondary period. Then followed, in 

 the Tertiary period, after the birth of Hawaii and Tahiti, and 

 when the island groups of the Western Pacific were mainly sub- 

 merged, the general dispersion from America of the Composita^, 

 Lobeliaceae, and other orders, now represented only by genera 

 peculiar to the Hawaiian and Tahitian islands. Last of all, 

 towards the close of the Tertiary period, when the island-groups 



