48 A NATURALIST IN THE PACIFIC CHAP. 



that grow at the borders of a mangrove-swamp in Fiji. Their 

 absence can scarcely be due to the want of suitable stations, as is 

 indicated by the common occurrence in the Tahitian coast-marshes 

 of Chrysodium aureum, the Great Swamp-fern, that not only 

 abounds in the mangrove belts of Fiji, Tonga, and Samoa, but is 

 associated with mangrove-swamps over much of the tropical zone. 

 Nor can it be said that the currents are ineffective, or that the 

 seeds or fruits of the missing plants possess, as a rule, insufficient 

 floating powers. Most of the plants of the Tahitian beaches hail, 

 like those of Fiji, from Malaya, and have been brought through the 

 agency of the currents ; and many of the absent littoral plants that 

 have the same home, such as Heritiera littoralis and Clerodendron 

 inerme, have fruits or seeds just as capable of floating unharmed 

 over the same extent of ocean. It is not any defect in floating- 

 power that has prevented the establishment of two such plants in 

 the Tahitian area. Entada scandens, which in some parts of the 

 world is a typical climber of the mangrove-formation, and in other 

 places thrives well in the absence of mangrove-swamps, has only 

 been recorded from Rarotonga in this region by botanists, but I 

 believe Wyatt Gill refers to its occurrence in Mangaia in one of 

 his books. 



On the other hand, it is likely that the floating seedlings of 

 Rhizophora and Bruguiera, which represent the only means of dis- 

 persal by the currents at the service of these mangroves, would not 

 arrive at Tahiti in a condition favourable for the establishment of 

 the plants. My observations, which are described in Chapter XXX., 

 go to show that, though the seseedlings will float uninjured in still 

 sea-water for months, they will not withstand prolonged sea-buffet- 

 ing. These two genera of mangroves, it is most important to 

 remember, supply the pioneers and the principal components of a 

 mangrove-swamp in the Western Pacific. Where they fail to 

 establish themselves, the requisite conditions for the large number 

 of plants and animals that find their home in and around a man- 

 grove-swamp would not be provided. We thus perceive that the 

 absence from the Tahitian coast flora of several plants that are 

 associated in Fiji with the mangrove-swamps depends on a law of 

 association, which has already been referred to in the preceding 

 chapter, and is not concerned with incapacity for dispersal by 

 currents (see Note 26). 



Whilst the Tahitian coast flora does not, therefore, possess the 

 plants of the mangrove-swamp and its vicinity, it includes most of 

 the typical beach-trees of the coral islands and reef-fronted coasts of 



