98 A NATURALIST IN THE PACIFIC CH. x. 



discussion of the buoyancy of seeds and fruits from the structural 

 standpoint. 



Summary of the Cliapter. 



(a) The great majority of seeds and seedvessels (quite 80 per 

 cent.) are much heavier than sea-water, but a noticeable proportion 

 are considerably lighter than fresh water, whilst those with a specific 

 weight near that of fresh water or of sea- water are very few. 



(fr) The buoyancy of seed and fruit has no direct relation to 

 the density of sea-water, and even if the ocean was deprived of all 

 its dissolved salts, the agency of the dispersal of plants by currents 

 would not be materially affected. 



(c) Small changes in sea-density, such as the physicist would 

 allow, would, therefore, have no appreciable influence on the opera- 

 tions of the currents as plant dispersers ; and only great changes 

 in density, such as are presented by the waters of the Dead Sea, 

 would add materially to the number of floating seeds and fruits. 



(d) Although the specific weight of seeds and fruits in its 

 relation to sea-density may be regarded as an accidental attribute, 

 their non-buoyancy in the great majority of plants has had a far- 

 reaching influence not only on plant-distribution, but on plant- 

 development. The plant-world would be transformed if all seeds 

 and fruits floated in sea-water. 



(e) If the floating seed or fruit displays a quality that, so far as 

 the density of the sea is concerned, has been developed in quite 

 another connection, we have next to inquire whether the structure 

 of such buoyant seeds and fruits also affords evidence of non- 

 adaptation. 



