392 GEOGRAPHICAL DISTRIBUTION. Chap. XII. 



what they are elsewhere. Such cases are generally ac- 

 counted for by the physical conditions of the islands ; 

 but tins explanation seems to me not a little doubtful. 

 Facility of immigration, I believe, has been at least as 

 important as the nature of the conditions. 



Many remarkable little facts could be given with 

 respect to the inhabitants of remote islands. For 

 instance, in certain islands not tenanted by mammals, 

 some of the endemic plants have beautifully hooked 

 seeds; yet few relations are more striking than the 

 adaptation of hooked seeds for transportal by the wool 

 and fur of quadrupeds. This case presents no difficulty 

 on my view, for a hooked seed might be transported to 

 an island by some other means ; and the plant then 

 becoming slightly modified, but still retaining its hooked 

 seeds, would form an endemic species, having as useless 

 an appendage as any rudimentary organ, — for instance, 

 as the shrivelled wings under the soldered elytra of 

 many insular beetles. Again, islands often possess trees 

 or bushes belonging to orders which, elsewhere include 

 only herbaceous species ; now trees, as Alph. de Can- 

 dolle has shown, generally have, whatever the cause 

 may be, confined ranges. Hence trees would be little 

 likely to reach distant oceanic islands; and an herb- 

 aceous plant, though it would have no chance of 

 successfully competing in stature with a fully deve- 

 loped tree, when established on an island and having 

 to compete with herbaceous plants alone, might readily 

 gain an advantage by growing taller and taller and 

 overtopping the other plants. If so, natural selection 

 would often tend to add to the stature of herbaceous 

 plants when growing on an island, to whatever order 

 they belonged, and thus convert them first into bushes 

 and ultimately into trees. 



With respect to the absence of whole orders on 



