182 ABSENCE OP TEERESTRIAL [Chap. XIIL 



where 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 suc- 

 cessfully competing with the many fully developed trees 

 growing on a continent, might, when established on an 

 island, gain an advantage over other herbaceous plants 

 by growing taller and taller and overtopping them. 

 In this 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 ani- 

 mals 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 Sey- 

 chelles. But I have already remarked that it is doubt- 

 ful 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 introduced into Ma- 



