310 THE VOYAGE OF H.M.S. CHALLENGER 



such an islet, which may be termed its growing edge, the vegetation is scanty, and there 

 are but few trees. A binding weed loosely covers a surface composed almost entirely of 

 sand, broken shells, and coral debris with pumice ; and it is on such an unproduc- 

 tive soil that the Casuarina and Pandani flourish. On the lee side of the islet, which is 

 the nucleus or oldest portion, from which the islet has been gradually growing seaward 

 with the extension of the reef, the soil contains a much larger proportion of humus, and 

 the vegetation is not only much denser, but is of a different character. Here, the trees 

 form a thick belt, their branches overhanging the rising tide. The commoner kinds are : 

 Barringtonia speciosa, Calophyllum inophyllum, Thespesia populnea, Hibiscus tiliaceus, 

 together with others, such as Cerbera odollam and Ochrosia parviflora. It is worthy of 

 note that the fruits of nearly all the trees mentioned as forming the margin of the vege- 

 tation, whether on the lee or weather side of such an islet, float in salt water. The small 

 cones of the Casuarina are, however, an exception, for they sink in salt water when they 

 are green, and require a certain amount of drying before they can be transported by the 

 tides and currents of the sea. Just within the line of trees that immediately borders the 

 beach, Cycas circinalis, Pandanus spp., Heritiera littoralis, Terminalia sp., and Cerbera 

 odollam commonly occur. With the exception of the fruits of the Cycas the fruits of all 

 these trees float in salt water, and occur abundantly in the vegetable drift. Out of ten 

 green fruits of the Cycas, all but one sank in salt water, yet this exceptional circumstance 

 sufficiently accounts for its occurrence on the coral islets. On the whole, my observations 

 prove that the waves afford the means of dispersal of all those trees in a coral islet which 

 line the shore, as well as of those which form a belt immediately within them. 



Proceeding further in from the beach towards the centre of the islet, huge banyans and 

 other trees having wide-spreading buttresses are met with ; many of which reach a height of 

 150 feet and upwards, and afford a home to numbers of fruit-eating pigeons, which largely 

 subsist on their fruits. Conspicuous amongst these trees is a species of Canarium, the 

 disgorged nuts of which frequently strew the ground beneath, a banyan (Ficus sp.), with 

 large oblong fruits, and another species with spherical fruits, a species of Eugenia, probably 

 a variety of Eugenia jambos, together with several others, the fruits of which were found in 

 the crops of pigeons shot, and a list of which is given below. The Fruit Pigeon, therefore, 

 is doubtless an active agent in the conveyance of seeds of such trees from island to island. 



The picturesquely wooded coral islets of these seas have thus been stocked through 

 two principal agencies. Winds and currents drift to their shores the fruits and seeds of the 

 littoral trees which ultimately form a belt, whilst the fruit pigeons disgorge the seeds or fruits 

 of those often colossal trees which occupy the interior. The same agencies co-operate in 

 the dissemination of the plants inhabiting the larger islands, where the littoral trees are 

 much the same. There are wide mangrove swamps on the coast, and lines of Ni/pa palms 

 edging the lower courses of the streams. In addition to those already mentioned, I 

 observed that the pigeons ate several others, including the flue laurel (Litsea sp.) dis- 



