248 



DISTRIBUTION OF PLANTS. 



On reviewing the vegetable growth on the thirty-three coral-islands 

 above described, the species of plants, about thirty-eight in number, 

 are probably no one of them peculiar, but are all East-Indian and sub- 

 maritime ; several however, extremely rare on the rocky groups and 

 hardly seen growing in mineral soil. On the other hand, certain 

 submaritime plants frequent in the mineral soil of the rocky groups, 

 did not occur on the low coral-islands. 



Independent of the character of the soil, coral-islands situated in the 

 midst of or in the close vicinity of rocky groups, partake of the vege- 

 table growth on those groups : as do the few coral-islands that have 

 been elevated, pushed up out of the ocean by geological causes. 



The low mid-ocean coral-islands are thus found to contain the same 

 set of plants in all parts of the Pacific ; and beyond these few ascer- 

 tained species, do not facilitate the transmission of seeds from one 

 rocky group to another. The coral-islands are therefore of no im- 

 portance in Botanical geography ; and being omitted, the rocky 

 groups of the Pacific resolve themselves into well-defined botanical 

 regions : 



1. The Taheitian Island-region. 



Returning now to the Order of our Voyage. On the 8th of Sep- 

 tember, 1839, the Vincennes sailing Westward along Rairoa, reached 

 at sunset the farther end ; and turning South, took leave of the Pau- 

 motu archipelago of low coral-islands. 



a. Metia. 



They who have long sailed among ring-shaped reefs can appreciate 

 the excitement produced on deck, at daybreak on the 9th, by the 

 announcement of a " real island." From the position, one hundred 

 miles North of Taheiti, clearly Metia, or Aurora Island. There stood 

 the land, high out of the water : yet there was something unusual in 

 its aspect ; explained on drawing near : the island, three or four miles 

 in length and width, proving flat-topped, abruptly-terminating all 

 around in a vertical cliff two hundred and fifty feet high ; or where the 

 base was in some places extensively undermined, actually out-hanging 

 over the ocean. 



