Formation of Forests 69 



stems are washed by the waves at high tide. The strand vegetation 

 on the south-west corner of Krakatau, where it is most widely spread, 

 is composed of elements of different ages, the oldest of which occur 

 for the most part toAvards the interior, the youngest nearer to the 

 tidal zone (see, for example, PI. V., fig. 5). This distribution of the 

 recent littoral flora over a relatively broad zone is most readily ex- 

 plained by the gradual growth of the island in the shore-region, a 

 gradual seaward extension of the shore-line in the course of years. 



Measurements taken by Verbeek proved that even during the first 

 few months after the eruption there were considerable alterations in 

 the sea-floor all round the Krakatau islands. Some of the pumice and 

 masses of ashes were carried hither and thither by high seas : some 

 sandbanks which were formed shortly after the outburst completely 

 disappeared, while in other places the light and easily moved material 

 was piled up into new submarine hills and banks or deposited on the 

 shores of the three islands. In this way the flat sandy shore has re- 

 ceived important additions on the south and west coasts of Krakatau 

 and on the south coast of Verlaten island. These accumulations of 

 material on the beach remain, though reduced in size. It is obvious 

 that the oldest strand-plants, which sprang from the seeds and fruits 

 from the drift formed in the first year, have been gradually separated 

 from the beach by a constantly increasing belt and that during this 

 shifting of the shore-line new plant-germs were introduced with the 

 pumice and took part in the formation of the present discontinuous 

 strand-forest. Other factors may of course have been concerned in 

 the building up of this forest, such as are responsible for the 

 spreading of the strand-plants above the normal drift-zone in coral 

 islands or other coast-lines, but these factors afford a less probable 

 explanation than that already suggested. It is, for example, hardly 

 conceivable, considering the present state of the fauna of Krakatau, 

 that fruits and seeds were carried inland from the drift-zone by 

 animal-agency. It has, however, elsewhere been shown that crocodiles, 

 lizards, and turtles, that is, animals of which some already occur on 

 the island, are of importance from the point of view of plant-dispersal. 

 Beccari states that lie found a large quantity of Pandanus fruits in 

 the stomach of Loplwra amboinensis, and that in Borneo certain 

 turtles constantly eat the fruits of a Durio and deposit the seeds 

 with their excrement. On the other hand the agency of crabs, by 

 which, according to Guppy, the germs of certain plants, especially 

 those of Morbida dtrifolia, Herncmdia peltata, and Cordia sitbcor- 

 data, have been spread over the interior of the Cocos islands, may be 

 disregarded, as the seeds and fruits (Cocos, Barringtonia, CalophyUvm, 

 Pandanus) which have been carried farther inland are those which 



53 



