NATURAL COLONISATION METHODS 289 



the trees tliat fringe tropical shores (and one of the most 

 notable features of tropical shores is the presence of dense 

 vegetation right down to the lap of ocean waves) have com- 

 plicated root systems, so that, above ground and below, the 

 trees tangle this way and that, and form inseparable masses. 

 The mangrove is a good example of this type of growth, for a 

 clump of trees will grow in so great a confusion of entangle- 

 ment that the separation of individuals may be impossible : 

 and, moreover, the whole will be firmly braced together by 

 creeping plants, which run from branch to branch like cordage 

 to the masts of ships. 



A scour of the sea-coast, or a river in flood by heavy rain, 

 may undermine such a clump, tear it away, and set it adrift 

 to sea, with all the earth still held in the meshes of the roots, 

 all the trees standing — a perfect " floating island." Such 

 things happen, and the floating island is a not uncommon 

 phenomenon in the straits and seas of the Malay Archipelago. 

 I know of a case, where, far out to sea, a submarine cable, on 

 being hauled to the surface, brought up with it banana trees 

 and portions of native houses, which had obviously gone to sea 

 as a floating island and had encountered shipwreck. 



It is easily seen that such an island might serve for the 

 transport of a very large number of colonists. It is possible 

 even that it carried human occupants. Such islands could 

 not be expected to long survive the waves of the Southern 

 Ocean, and disaster would surely overtake them when they 

 had left the calmer landlocked seas of the Archipelago. But 

 some portion of them, crowded with the survivors of the wreck, 

 may float for long, and carry its living burden to new homes. 



The trunks of trees are common on the seaward beaches 

 and each may have carried its passenger to the atoll from 

 some distant coast-line where its voyage was started. There 

 is one peculiarity about many of these trees which makes 

 them well adapted to the carrying of Nature's colonists. This 

 peculiarity is the shape of the lower portions of their trunks. 

 • Most of the tropical trees, whose wood is not especially hard, 

 and which often grow to a great height, have very strong 



