182 ABSENCE OF TEREESTRIAL [Chap. XIH. 



elsewhere include only herbaceous species ; now trees, 

 as Alph. de Candolle has shown, generally have, what- 

 ever the cause may be, confined ranges Hence trees 

 would be little likely to reach distant oceanic islands'; 

 and an herbaceous plant, which had no chance of 

 successfully competing with the many fully developed 

 trees growing on a continent, miglit, when established 

 on an island, gain an advantage over other herbaceous 

 plants by growing taller and taller and overtopping 

 them. In tliis case, natural selection would tend to 

 add to the stature of the plant, to whatever order it 

 belonged, and thus first convert it into a bush and then 

 into a tree. 



Absence of Batrachians and Terrestrial Mammals on 

 Oceanic Islands. 



With respect to the absence of whole orders of 

 animals on oceanic islands, Bory St. Vincent long ago 

 remarked that Batrachians (frogs, toads, newts) are 

 never found on any of the many islands with which the 

 great oceans are studded. I have taken pains to verify 

 this assertion, and have found it true, with the ex- 

 ception of New Zealand, New Caledonia, the Andaman 

 Islands, and perhaps the Salomon Islands and the 

 Seychelles. But I have already remarked that it is 

 doubtful whether New Zealand and New Caledonia 

 ought to be classed as oceanic islands ; and this is still 

 more doubtful with respect to the Andaman and 

 Salomon groups and the Seychelles. This general 

 absence of frogs, toads, and newts on so many true 

 oceanic islands cannot be accounted for by their 

 physical conditions : indeed it seems that islands are 

 peculiarly fitted for these animals ; for frogs have been 



