196 A NATURALIST IN THE PACIFIC CHAP. 



to dispersal they must be disregarded. The buoyancy of the seeds 

 and their well established distribution by currents render unneces- 

 sary an appeal to the floating pod. 



The following is a summary of the foregoing remarks on 

 Csesalpinia bonducella and C. bonduc. 



(1) The two species in Fiji are not always sharply distinguished, 

 since intermediate forms occur, and here probably lies the explana- 

 tion of the confusion that has sometimes occurred in diagnosing the 

 species. 



(2) Both are typical littoral plants, distributed over most of the 

 tropical zone, and occurring in company in most of the Pacific 

 archipelagoes ; but they at times extend far inland. 



(3) Though it is not unlikely that sea-birds may have aided in 

 their dispersal, the oceanic currents have been the great agencies in 

 their dispersal, as is indicated by the frequent transport of seeds 

 In the Gulf Stream drift across the Atlantic, and by their occur- 

 rence in beach drift in various parts of the world. 



(4) Having regard to the present arrangement of the currents 

 and the distribution of the two species, reasons are given for the 

 belief that their original birthplace was in the interior of the 

 American continent. 



(5) Notwithstanding the stony hardness of the seeds, when a 

 notch is made in the outer skin a seed rapidly takes up water, and 

 in a few days it becomes a soft and much swollen germinating 

 mass. The author is inclined to think that this was the original 

 condition of the seed, and that the rest-stage is an adaptation 

 to secular differentiation of climate in later epochs. 



(6) Unlike the seeds of other Leguminous littoral plants, those 

 of Caesalpinia are not likely to germinate abortively when floating 

 in warm tropical seas, a risk that restricts the distribution of several 

 littoral species. 



(7) As tested by experiment, the seeds of both species are often 

 able to float unharmed for years ; but on the other hand seeds not 

 infrequently have no floating power. 



(8) Observation, however, shows that buoyancy goes with 

 station, and that the general rule here applies that the seeds of 

 coast plants float and those of inland plants sink. 



(9) The nature of the influence of " station " on the seed- 

 buoyancy is obscure ; but it is evidently not connected with the 

 usual differences between coast and inland localities, such as those 

 concerned with exposure or shade, dryness of soil, relative humidity, 

 and similar contrasts. 



