4IO A NATURALIST IN THE PACIFIC ch. xxvn 



highly variable plant is an important factor in the development of 

 peculiar species in the different groups, just as it has been shown to 

 be in the previous chapter in the case of genera dispersed over the 

 whole Pacific. The role of the polymorphous species has always 

 been an important one in this region. 



(7) In the case of several Fijian genera it seems almost futile 

 to talk of existing means of dispersal, since the present distribu- 

 tion of genera like Sterculia and Gnetum, that occur on both 

 sides of the Pacific, in America and in Asia, is not to be thus 

 explained. 



(8) On account of the large size of their seeds and " stones " 

 it might be argued that certain of the Fijian plants afford evidence 

 of a previous continental condition of the islands of the Western 

 Pacific, since it is not easy to understand how such large seeds and 

 "stones" could have been transported over broad seas by birds. 

 It is, however, pointed out that in these respects the species of 

 a genus may vary greatly, and that the seeds and stones may be 

 large in some species and small in others. 



(9) The greater number of the genera that have entered the 

 Pacific from the Old World have not advanced eastward of the 

 Fijian region, half of the Fijian genera not occurring in the 

 Hawaiian and Tahitian regions ; and the explanation of this is to 

 be found not in any lack of capacities for dispersal, but in a want 

 of opportunities. The story of plant-distribution in the Pacific is 

 bound up with the successive stages of decreasing activity in the 

 dispersing agencies. The area of active dispersion that at first 

 comprised the whole of the tropical Pacific was afterwards restricted 

 to the South Pacific, and finally to the Western Pacific only. The 

 birds that in an early age carried seeds all over this ocean became 

 more and more restricted in their ranges, probably on account of 

 increasing diversity of climatic conditions. The plants of necessity 

 responded to the ever narrowing conditions of bird-life in this 

 ocean, and the differentiation of the plant and of the bird have 

 taken place together. 



