xxvn TAHITIAN GENERA 381 



investigated, it is likely that much of the difficulty will disappear. 

 Hawaii, as we have before seen, abounds with perplexing questions 

 of this nature. When dealing with the absentee Tahitian genera, 

 later on in this chapter, it will be shown that " size " has played a 

 prominent determining part in the exclusion of genera from 

 Tahiti, genera with seeds or " stones " exceeding half an inch or 

 twelve millimetres in dimension being, as a rule, unrepresented 

 amongst the truly indigenous plants. 



My further remarks on these Tahitian genera found in Fiji but 

 not in Hawaii will be limited to some general observations from 

 the standpoint of dispersal. I will first discuss some of those 

 genera that possess only peculiar species. They belong to an era 

 of dispersal that, as far as Tahiti is concerned, is passing or has 

 passed away. Here we have the species of each genus more or 

 less localised in the various South Pacific archipelagoes ; but, as 

 with Meryta, Alstonia, and Loranthus, it is often apparent that, 

 although the Tahitian region is mainly outside the zone of present 

 dispersal, the different groups of the Western Pacific are kept in 

 touch by the possession of species in common. This testifies to 

 the activity of dispersal in that region after it had become sus- 

 pended in Eastern Polynesia. The connection between the isolated 

 endemic species of Eastern Polynesia and a species ranging over 

 the Western Pacific can sometimes be shown, as in the case of 

 Loranthus, where a species confined to the Society Islands and to 

 the Marquesas is very closely related to L. insularum, a widely- 

 ranging West Polynesian species that reaches eastward as far as 

 Rarotonga. 



We next have those genera like Grewia, Nelitris, Melastoma, 

 Randia, Geniostoma, Tabernasmontana, Fagraea, Bischoffia, Maca- 

 ranga, and Ficus, that possess in Polynesia one or more widely- 

 ranging species. The agency of the polymorphous species, which 

 I have described in the preceding chapter in connection with the 

 general dispersal of Malayan plants over the whole of Polynesia, 

 is evidently also active when the work of dispersal is restricted to 

 the South Pacific. Its operation is to be distinctly traced in all 

 the genera above named except in Fagraea and Ficus. Thus, in 

 the genera Grewia, Melastoma, Randia, Geniostoma, and Macaranga 

 we find a single variable species ranging over the South Pacific 

 from Fiji to Tahiti, keeping all the groups in touch, but associated 

 in each, as a rule, with one or more peculiar species. A yet earlier 

 stage in the process is to be seen in those genera which, like 

 Nelitris, Tabernaemontana, and Bischoffia, possess only a solitary 



