124 A NATURALIST IN THE PACIFIC chap. 



concerned itself with placing plants of xerophilous habit possess- 

 ing buoyant seeds or fruits at the coast. Under such conditions we 

 would now and then expect to find an inland plant possessing 

 buoyant fruits or seeds of this description that has never been able 

 to establish itself at the coast. 



A good instance is afforded by Pritchardia Gaudichaudii, a fan 

 palm peculiar to Hawaii, the drupes of which float for several 

 weeks and have a covering of spongy buoyant tissue (see Chapter 

 XXV.). The seeds of Hibiscus Abelmoschus, a species dis- 

 tinguished subgenerically from the littoral Hibiscus tiliaceus^ 

 offer another example. They float for months, and owe their 

 buoyancy to a layer of air-bearing tissue between the kernel and 

 the test, in this respect differing from the seeds of the littoral 

 species, where the floating power is due to unoccupied space in the 

 seed-cavity. The buoyancy of the seeds of Hibiscus Abelmoschus 

 thus offers another example of ineffectual floating power, since it 

 is not a littoral plant, is often cultivated, and has accompanied 

 aboriginal man over much of the tropical zone. 



A singular instance of the dispersal by currents of an inland 

 plant that occurs both wild and cultivated in tropical America, the 

 West Indies, and on the West Coast of Africa, is afforded by 

 Spondias lutea, Linn., which is referred to at the end of Chapter 

 XXXII. Its "stones," which are provided with a cork-like cover- 

 ing much as we find with those of Cordia subcordata and Guettarda 

 speciosa, possess great buoyancy, and are found in the river and 

 beach drift of those regions with the seeds in a sound condition. 



A very remarkable case of ineffectual buoyancy is presented 

 by the seedvessels of Brackenridgea, which have been found 

 floating in the drift off the coast of New Guinea. They owe their 

 floating power to closed cavities which would seem to arise from 

 the failure of one of the seeds or from the abortion of an ovule. 

 But, according to Beccari, their fleshy coverings would aid their 

 dispersal by frugivorous birds ; and since the species are all much 

 localised and are rarely littoral in their habit, it is very probable 

 that birds have mainly effected the dispersal of the genus (see 

 Note 46). It has, however, been shown in the previous chapter 

 that Premna taitensis and Morinda citrifolia owe their dispersal by 

 currents to similar cavities in the seeds or " stones." 



Amongst the inland plants possessing seeds or fruits that are 

 dispersed by the currents without aiding the distribution of the 

 species may be recognised types of both the adaptive and non- 

 adaptive groups. A singular instance is afforded by the large 



