CH. XXXIII SEED-DISPERSAL AND GEOLOGICAL TIME 503 



of the Western Pacific had re-emerged, a general dispersion of 

 Old World plants, mainly Malayan, took place over all the present 

 archipelagoes of the tropical Pacific. 



Since the climate of Hawaii must have, to a great extent, 

 shared in the vicissitudes of the continental climates of the 

 northern hemisphere before, during, and after the Glacial epoch, 

 it is assumed that in the Ice Age no tropical plants reached the 

 group, and that only the plants now represented in its mountain- 

 flora could have then reached there. The area of active dispersion 

 of tropical plants was pushed far south. During the Ice period, 

 Indo-Malayan plants doubtless crowded into the equatorial region 

 of the Western Pacific ; but, cramped and confined within this 

 limited area, they were cut off by a climatic barrier from the cool 

 latitudes of Hawaii. As the cold ages passed away, migratory 

 birds, confined during that period to the southern hemisphere, 

 would extend their ranges north, sometimes reaching Hawaii, and 

 transporting to it the seeds of New Zealand and Antarctic genera, 

 now represented by endemic species on its mountain-slopes. The 

 Indo-Malayan plants, with the increasing warmth in the climate of 

 the northern hemisphere, would overrun the Pacific, set free from 

 their prison in the south-west portion of that ocean. Dispersal, we 

 might imagine, would be at first very active over the whole ocean. 



My point is, then, that whilst the Malayan era of the plant- 

 stocking began after the Ice Age in the northern hemisphere, the 

 dispersion of the New Zealand and Antarctic genera over the 

 Pacific took place during that period ; whilst, as before noticed, the 

 dispersion of the Compositae, Lobeliaceae, and other orders, repre- 

 sented now in Hawaii by endemic genera, would be pre-Glacial 

 and well back in the Tertiary epoch. I would, therefore, suggest 

 the following scheme, in illustration of the floral history of the 

 tropical Pacific. 



(i) The Age of Conifers of the Western Pacific during the 

 Mesozoic period, and before the appearance of the Hawaiian and 

 Tahitian archipelagoes. 



(2) The Age of Composite and Lobeliaceae, and of other 

 genera. This is an era of American plants, and it is referred to 

 the Tertiary period. In it only the newly-formed Hawaiian and 

 Tahitian groups shared, the islands of the Western Pacific being 

 largely submerged. 



(3) The Age of Malayan plants, regarded as mainly post- 

 Glacial, and subsequent, therefore, to the re-emergence of the 

 Western Pacific islands at the close of the Tertiary period. 



