xxvn PERMANENT INSULAR CONDITIONS 381 



the distribution of Dammara may, however, be fairly claimed on 

 their behalf. 



The dilemma into which such discussions lead us is aptly 

 stated by Dr. Pilsbry. If we do not accept the hypothesis of a 

 Pacific continent, we have to explain the cessation of the means 

 of transportal in later geological times, since this is implied in the 

 isolation necessary for the development of peculiar characters in a 

 fauna or a flora. This was the dilemma that presented itself to 

 me in studying the origin of the Fijian plants. Assuming on 

 geological grounds that the insular condition had been always 

 maintained I had to explain the differentiation in the inland 

 plants, or in other words to account for the failure of the means of 

 transportal that once existed. Since this subject bears directly on 

 the past condition of the Fiji Islands, I may be pardoned for 

 referring to it here. It belongs properly to the second volume 

 which it is proposed to devote to the dispersal and distribution of 

 Pacific plants ; but as I contest the pre-existence of a Pacific 

 continent, it is fitting though not necessary that this difficulty 

 should be faced at once. 



If we in imagination combine in a typical island the characters 

 of the flora presented by islands of different elevation in the 

 Pacific we get a result of this kind in an island of the height of 

 Hawaii, nearly 14,000 feet. The littoral plants of such an island 

 are found all over the coasts of the tropical Pacific, and for the 

 explanation of this fact we look mainly to the agency of the 

 ocean-currents. The plants of the mountain summit, belonging to 

 the temperate genera of Geranium, Rubus, Ranunculus, Vaccinium, 

 &c., are represented at least generically on the tops of the lofty 

 ranges of the Pacific coasts and in the interior of the continents ; 

 and we find the explanation of the wide diffusion of such plants 

 in the agency of the migrant birds that at no distant time, if not 

 actually in our own time, were regular visitors to these mountain 

 regions. The plants of the marsh, of the stream, and of the pond, 

 belong often to species that occur in similar stations over a great 

 portion of the world, such as species of Drosera, Ruppia, Pota- 

 mogeton, &c. ; and here the agency of wild duck and other water- 

 fowl may be observed in active operation. 



But when in such an island we regard the intermediate region 

 between the uplands and the coast, usually the forest-zone, we 

 find an area of change not only for the plants but also for the 

 birds. It is here that the new genera of plants have been developed 

 that distinguish the floras of the Pacific groups each from the 



