XVI LITTORAL AND INLAND PLANTS' RELATIONSHIP 165 



The seeds either sink at once or in the course of a day or two ; 

 whilst the pods or their fragments float at first in sea-water, but all 

 are at the bottom in a week or less. With its absence of any- 

 apparent means of dispersal this small tree presents quite an 

 anomaly in the strand-floras of the Western Pacific, and can only 

 be regarded as a loan from the inland flora, though probably of a 

 very ancient date, and perhaps going back like Acacia koa, the 

 forest-tree of Hawaii, to some early epoch in the history of these 

 islands. 



The conclusions to be drawn from the discussion of the relations 

 between the littoral and inland species of the same genus in 

 the Pacific islands. (Chapters XIV., XV., XVI.) 



In ten of the twenty-two genera here dealt with (Calophyllum, 

 Hibiscus, Colubrina, Morinda, Scaevola, Cordia, Ipomea, Vitex, 

 Tacca, Casuarina) the shore and inland species have their own 

 independent modes of dispersal, usually by currents in the case of 

 coast plants, and by birds in that of inland plants ; and the 

 relations between the two are not such as to suggest a derivation 

 of one from the other. 



In six genera the inland species are regarded as derived from 

 the littoral species. In two of them, as in Vigna and Premna, 

 where the coast and inland species occur in the same group of 

 islands and are connected by intermediate forms, there is direct 

 evidence in favour of this conclusion ; but such a development 

 of inland species need not have taken place in every group, since 

 in the instance of Premna it has apparently occurred only in 

 the Western Pacific, and the inland and coast species have 

 extended independently to the eastern groups through the agencies 



of birds and currents In the other four genera (Canavalia, 



Erythrina, Sophora, Ochrosia) we have presented the so-called 

 " Hawaiian difficulty," that group being alone concerned. Although 

 these genera have no littoral species in Hawaii, they have inland 

 species in those islands, which are in three genera endemic. Since 

 these inland species have non-buoyant seeds or seedvessels, the 

 transport of which by birds half-way across the Pacific Ocean is in 

 the case of the first three genera unlikely and in the last impossible, it 

 is assumed that they are all derived from original coast species with 

 buoyant seeds or fruits, such as are widely distributed over the 

 Pacific but are not now existing in Hawaii. This assumption, 

 in the instance of the Leguminosse, to which the first three genera 



