120 A NATURALIST IN THE PACIFIC chap. 



hampered by conditions not of its own creation, and that twO' 

 opposing forces are ever at work, the one creating and the other 

 limiting the creative power, the actual mode of dispersal being but 

 a blind and accidental result of the struggle. 



The question of the operation of Natural Selection is not raised,^ 

 as Professor Schimper indicates, until we consider whether the new 

 function has had any bettering influence on the structure or 

 mechanism with which it has come to be concerned. If such a 

 modification is thus brought about it might be legitimately claimed 

 as a result of this agency, and the term "adaptation" could be 

 used. But if there is no evident change produced, we should be 

 compelled to assign very subordinate limits to the capacity of 

 Natural Selection ; and in the instance of buoyant fruits and seeds 

 it would be restricted to determining a plant's station by the water- 

 side and in increasing its area. It is only in the first case that we 

 could speak of them as adaptations in the meaning attached to this 

 term in the language of the Selection Theory. It would at first 

 sight seem easy to ascertain whether the characters of fruits and 

 seeds, to which the buoyancy is due, are adaptations in this sense 

 of the word ; but in reality it is far from being so. We can, how- 

 ever, proceed with unanimity up to a certain stage in the argument ; 

 but there agreement ends. 



It has been before established that in the Pacific islands, and 

 indeed in the tropics generally, the plants with buoyant seeds or 

 seedvessels are mainly stationed at the coast. It has also already 

 been shown that this littoral station is often associated with a 

 special buoyant-tissue in the coverings of the seed or fruit ; and it 

 will now be pointed out that this tissue is, as a rule, absent or but 

 scantily developed in the case of inland species of the same genus. 

 Of great importance, remarks Professor Schimper (p. 179), in 

 relation to the Selection Theory and the development of adapta- 

 tions, is the comparison of the fruits and seeds of strand-plants 

 with those of allied inland species ; and he finds here evidence in 

 support of the Darwinian view. He takes the cases of the genera 

 Terminalia and Calophyllum, which contain both inland and littoral 

 species ; and he shows that although the same buoyant-tissue occurs 

 in the fruit-coats of inland species, it is there much diminished, and 

 in consequence the floating powers are considerably lessened or lost 

 altogether (see Chapter II.). It is not pretended that this tissue 

 has had any connection in its origin with dispersal by currents, but 

 merely that its greater development in the shore species is an 

 adaptation to this mode of transport. 



