x THE BUOYANCY OF SEEDS AND SEEDVESSELS 97 



place, as has been often remarked in these pages, we have a wide 

 distribution generally associated with considerable buoyancy 

 of the seeds or fruits. In the second case the areas are usually 

 very restricted and there is little or no buoyancy. The better 

 fitted a seed or fruit is for dispersal by currents the greater, there- 

 fore, is the area of the plant. Whether such an important relation- 

 ship depends on an accidental attribute of the seed or fruit is the 

 question that immediately presents itself. But it is obvious that 

 in raising such a question we touch on a very vital point in 

 adaptation, since if attributes developed in one connection have a 

 profound influence in another we may have to rearrange some of 

 our fundamental notions of the inner workings of Nature. 



Let us, therefore, look a little closer into this matter, and turn 

 again to the Pacific islands. The present state of things may be 

 thus tersely described. Whilst the shore-plants dispersed by the 

 currents have remained relatively the same, changes of all kinds, 

 from the production of a variety and of a species to the develop- 

 ment of a genus, have taken place in the inland floras. Now, let 

 us imagine that all this is altered and that every seed or fruit is 

 buoyant. There would then be but little distinction between the 

 strand and inland floras, since they would be in a constant state of 

 interchange, and most species would be widely distributed. A 

 relatively monotonous aspect would belong to all insular floras, and 

 indeed to much of the plant-world, since isolation, one of the 

 principal conditions for the origin of new species and new genera, 

 would often not exist. 



On the other hand, let us suppose that all seeds and fruits 

 were non-buoyant. The agency of birds would then be alon e 

 available for stocking new islands with most of their plants. The 

 conditions of isolation would be intensified. There would be no 

 widely-ranging strand-flora, since every island and every stretch of 

 continental sea-board would possess its own littoral plants that 

 could only reflect the peculiarities of the inland flora. The only 

 determining factor between coast and inland plants would be the 

 presence or absence of the capacity or organisation for occupying 

 a station on the sea-shore. 



We have now proceeded far enough to disclose the far-reaching 

 influence on plant-distribution and on plant-development that the 

 relation between the specific weight of seeds and fruits and the 

 density of sea-water must possess. Yet it has been shown that 

 when such a relation is viewed statistically it has an accidental 

 aspect. We will accordingly devote the next few chapters to the 

 VOL. II H 



