3o6 A NATURALIST IN THE PACIFIC ch. xxiv 



(Swamp-Hens or Purple Water-Hens) have taken a prominent 

 part. 



(5) In the possession of species of the three genera of Conifera^, 

 Dammara, Podocarpus, and Dacrydium, which often largely form 

 the forests of the mountain-slopes, Fiji is distinguished from all the 

 other groups of the open Pacific with the exception of Tonga, 

 which owns a species of Podocarpus probably introduced by birds. 

 From the circumstance that Dammara has no known means of 

 crossing a tract of ocean, whilst Podocarpus and Dacrydium could 

 be dispersed by frugivorous birds, all three genera having, however, 

 much the same limited distribution in the Western Pacific, it 

 is apparent that something more than a question of means of 

 dispersal is here involved. It is assumed that they mark the site 

 of a Mesozoic continental area in this region, and that at this period 

 the Tahitian and Hawaiian groups which possess no Conifers did 

 not exist. This area was submerged during the Tertiary period 

 with the exception of a few peaks that formed small islands 

 on which the Conifers held their ground. During the Tertiary 

 submergence of the Western Pacific region, the Hawaiian and 

 Tahitian islands were built up by subaerial volcanoes and received 

 the ancestors of the Compositae and Lobeliaceae that now exist as 

 endemic genera in those groups. Then followed the emergence of 

 the islands of the Western Pacific and their occupation mainly by 

 Indo-Malayan plants that extended eastward over the Pacific. 

 Thus in the Pacific there has been first an age of Conifers in which 

 the islands of the Hawaiian and Tahitian regions could not partici- 

 pate, since they did not exist. Then ensued an era of American 

 forms of Compositae and Lobeliaceae in which only Hawaii and 

 Tahiti participated, since the Western Pacific region was sub- 

 merged. Lastly came the invasion of Indo-Malayan plants, which 

 have largely occupied every group in the tropical Pacific. 



