XIV LITTORAL AND INLAND PLANTS' RELATIONSHIP 133 



composition than the mangrove-formation, it is not to be assumed 



that in the Pacific region or in the tropics generally it is at all 



modern in its character. Though in the main, no doubt, more 



recent than the mangroves, since it is likely that in early 



geological periods the swamp rather than the sandy beach formed 



the predominant feature of the sea-border throughout the tropics, 



yet it bears in several respects the impress of a high antiquity. 



There are few beach plants in the tropical Ficific that are not 



found over the tropics of a large portion of the globe, a 



circumstance that would in itself warrant our assigning a great age 



to the beach-flora ; and it is highly probable that some at least of 



the beach plants of the Pacific that occur on the east and west 



coasts of tropical America are, for reasons given in Chapter XXXII., 



older than the barrier now interposed by Central America beLween the 



Atlantic and Pacific oceans. There are, it is true, a few species, 



like Acacia laurifolia and Drymispermum'^Burnettianum, which, on 



account of their restriction to the beaches of the Western Pacific 



and their lack of capacity for dispersal by currents, may be 



regarded as local productions ; but for the great majority, ranging 



as they do over much of the tropics, it is not possible to determine 



when and where they assumed their littoral habits. That except 



in a few instances their home in some bygone age lay outside the 



Pacific can scarcely be doubted. 



It is therefore to be expected that in a discussion of the relation 

 between the strand and inland floras in the Pacific islands the 

 problem will be mainly concerned with the possible derivation of 

 inland from littoral plants. In such a discussion the relation 

 between the beach and inland species of the same genus becomes a 

 subject of great interest. It is a subject that had a peculiar 

 fascination for Professor Schimper, who refers to it more than once 

 in his pages ; and though never able to take it up, he viewed it 

 as a very promising field of inquiry. The question has been 

 frequently alluded to in this work ; and it is especially dealt with 

 in one connection in Chapter II. It is there shown that whilst, as 

 a general rule, the seeds or seedvessels of the coast species possess 

 great floating power, those of the inland species of the same genus 

 have little or none, and that both may have independent modes of 

 dispersal, the first by currents, and the last through frugivorous birds. 

 A close connection between the beach and inland floras is 

 apparently displayed in the circumstance that quite a third of the 

 genera of the Pacific insular floras containing littoral species (some 

 70 in all, excluding the mangroves) possess in this region also 



