1 68 A NATURALIST IN THE PACIFIC CHAP. 



the inland flora of every region, whilst in the tropics the pre- 

 dominant plants are those ranging far and wide on the shores of 

 the warm regions of the globe. 



(3) Regarding the tropical strand-flora as comprising two forma- 

 tions, that of the beach and that of the mangrove swamp, the last, 

 which is the older of the two, may, it is suggested, be viewed as the 

 remnant of an ancient flora widely spread over the lower levels and 

 coastal regions of the globe, during an age when, in a warm 

 atmosphere charged with watery vapour and heavy with mist and 

 cloud, vivipary or germination on the plant was not the exception 

 but the rule. 



(4) But it is contended that even in the beach formation 

 some of the plants may date back to this age of vivipary, as is 

 indicated by the anomalous seed-structures of some of the genera, 

 such as Barringtonia, which seem to indicate a lost viviparous 

 habit. 



(5) Since the beach formation of the islands of the tropical 

 Pacific is largely formed of plants ranging over great areas in the 

 tropics, there is no reason to expect that it owes much to recruits 

 from the inland floras of this region. The discussion, therefore, of 

 the relation between the littoral and inland floras is mainly 

 concerned with the possible origin of inland from coast plants 

 in these islands. 



(6) Yet there are numerous cases of genera possessing both 

 coast and inland species that are of peculiar interest in determining 

 the true relation between the beach and inland floras. 



(7) As the result of a detailed discussion of these genera, 

 the conclusion is formed that the beach and inland floras have 

 been in the main developed on independent lines, the beach flora 

 receiving from the inland flora but few recruits, and except in 

 Hawaii yielding but few plants to the inland flora. Only a third 

 of the genera of the beach flora have also inland species, and in 

 only a few of these genera, or about a seventh of the whole beach 

 flora, can any question of a connection between coast and inland 

 species of the same genus be raised. 



(8) Two special difficulties arise in this discussion. The first is 

 the " Hawaiian difficulty," which is more particularly concerned 

 with genera of the orders Leguminosae and Apocynaceae. Here are 

 genera which possess both inland and littoral species, but only the 

 first occur in Hawaii. In the absence of any likely means of 

 dispersal, whether by currents or by birds, it is assumed that 

 the inland species are derived from shore plants, originally brought 



