128 A NATURALIST IN THE PACIFIC chap. 



(4) It is held by Professor Schimper that the structures con- 

 nected with the buoyancy of the fruits or seeds of several tropical 

 littoral plants are, in the above sense, adaptations ; and he points 

 to several genera where the buoyant tissues in the coverings of the 

 fruits or seeds of the coast species are scantily represented or 

 absent in the inland species of the same genus, a difference 

 corresponding with the loss or diminution of the floating powers. 



(5) This contrast in structure and in floating capacity between 

 the fruits or seeds of inland and coast species of the same genus is 

 beyond dispute, and the author adduces fresh data in support 

 of it. 



(6) But he contends that it is not proved that the relatively 

 great development of buoyant tissues in the case of littoral plants is 

 the effect of adaptation ; and that if the selecting process had been 

 confined to sorting out the xerophilous plants with buoyant seeds 

 or fruits and to placing them at the coast, the same contrast 

 would have been produced. 



(7) In support of this contention he points out that when such 

 littoral plants extend inland the floating capacity and the buoyant 

 tissues are as a rule retained ; and that in those exceptional cases 

 where inland plants possess buoyant fruits or seeds these tissues 

 are sometimes well developed under conditions in which they could 

 never aid the plant's dispersal. 



(8) But the most serious objection against the adaptation 

 view is that admittedly only about half of the shore-plants with 

 buoyant fruits or seeds come within its scope. Therefore a 

 second explanation has to be framed for the other plants 

 concerned. 



(9) As showing the difficulties raised by regarding some of the 

 structures connected with buoyancy as " adaptive " and others as 

 " accidental," it is pointed out that some fruits possess the two 

 kinds of structure. It is also shown that in several cases fruits 

 endowed with buoyant tissues are just as well adapted for 

 dispersal by frugivorous birds ; and the instance of Ximenia 

 americana is cited where a drupaceous fruit, known to be dispersed 

 by fruit-pigeons, possesses also in its " stone " both the " adaptive " 

 and " non-adaptive " types of " buoyant structures." 



(10) It is urged that whatever is the relation between the 

 buoyancy of the seeds and fruits of shore-plants and dispersal by 

 currents, there has been a uniform principle affecting all. 



(11) The weight of evidence is regarded as adverse to the 

 Natural Selection theory, an inference which is consistent with the 



