i82 A NATURALIST IN THE PACIFIC chap. 



power, the buoyancy arising from a large central cavity produced 

 by the shrinking and bending outward of the cotyledons during the 

 drying and hardening of the maturing seed (see figure in 

 Chapter XII). With the seeds that sink, this cavity is, as a rule, 

 reduced to small dimensions, and may be represented only by a 

 narrow slit. In some cases, however, where the cotyledons are un- 

 usually thick and heavy, even a large central cavity will not give 

 floating power to the seed. There is an indication in my experi- 

 ments that seeds from inland plants that have matured their pods 

 in the forests sink in a much greater proportion than seeds of coast 

 plants, or of those growing on the banks of estuaries. This we 

 might expect, since in the shade of the forests the drying process 

 that accompanies the setting and final maturation of the seed would 

 be less complete and the intercotyledonary cavity smaller than with 

 the seeds matured in more exposed situations. This is a point 

 however, that requires further investigation. 



It will thus be seen that in respect of buoyancy the seeds of 

 Entada scandens are to be referred to the mechanical or non- 

 adaptive group of buoyant seeds, described in Chapter XII, which 

 comprises several other Leguminous strand-plants, including 

 Csesalpinia bonducella. I especially studied the various stages in 

 the development of the buoyancy of seeds in this mechanical group 

 in the case of the species of Caesalpinia just named, and the 

 •description of the process as given under that plant will apply 

 to all. 



Summary relating to Entada scandens 



(i) This plant, which has been distributed by the currents over 

 the tropics of the globe, has its station in the mangrove swamp, on 

 the beach, by the estuary, and in the inland forest. 



(2) It is regarded as an American plant that has reached the 

 shores of the Indian Ocean by crossing the Pacific, and the coast 

 of West Africa by crossing the Atlantic. 



(3) Its occurrence on both coasts of America is attributed to 

 its having a focus of dispersal in the forests of Central America, 

 from which its seeds have been transported by the rivers to the 

 shores of the Atlantic and Pacific Oceans. 



(4) Its irregular distribution in the Pacific islands, to wit, its 

 absence from Hawaii and its rarity in the Tahitian region, is not to 

 be easily explained, but it is more than likely that it will be sub- 

 sequently recorded from other localities in Eastern Polynesia. 



