516 A NATURALIST IN THE PACIFIC CHAP. 



mangrove-swamp, and those of intermediate stations on the borders 

 of the swamps. The great majority of the Fijian shore-plants are 

 dispersed by the currents. The Tahitian Islands, which are repre- 

 sentative of Eastern Polynesia, lack the mangroves and most of 

 the plants that grow at the margin of a mangrove-swamp ; and 

 their strand-flora is mainly composed of plants of the beach, such 

 as are dispersed by the currents far and wide in tropical regions. 

 The Hawaiian strand-flora is very meagre in its character, lacking 

 not only the plants of the mangrove and intermediate formations, 

 but almost all the large-fruited beach-trees of the South Pacific. 

 Since Hawaii possesses but few current-dispersed shore-plants 

 that are not found in the New World, reasons are given for the 

 inference that such shore-plants were originally brought by the 

 currents from America, and not from the South Pacific. 



We are led on various grounds to the conclusion that tropical 

 shore-plants distributed by currents belong to two great regions, 

 the American including the west coast of Africa, and the Asiatic, 

 or Old World Region, which includes the African east coast. It 

 is held that America is so placed with regard to the currents, that 

 it is a distributor, and not a recipient of tropical shore-plants 

 dispersed by that agency. From this it follows that all cosmo- 

 politan tropical beach-plants that are dispersed by the currents 

 have their homes in America. 



The results of observation and experiment are given to show 

 that there is no direct relation between the specific weight of seeds 

 and fruits and the density of sea-water. Yet, although the floating 

 or sinking of a seed or fruit is but an accidental attribute, it has 

 had indirectly a far-reaching influence not only on plant-distribu- 

 tion, but on plant-development. In accordance with this want of 

 relation between the specific weight of seeds and fruits and the 

 density of sea-water, the great variety of structures concerned with 

 buoyancy are regarded in the main, after a detailed examination 

 of their character, as not arising from adaptation. Rather, it is 

 urged, is buoyancy connected with structures that now serve a 

 purpose for which they were not originally developed. Nature, it 

 is held, has never concerned herself directly with providing means 

 of dispersal of any sort. 



In the discussion of the relation between the littoral and inland 

 Pacific floras, it is shown, as a result of the examination of those 

 genera possessing both shore and inland species, that they have 

 been on the whole developed on independent lines. Two special 

 difficulties in explaining the modes of dispersal of plants of the 



