Ocean-currents 57 



of origin, the island of Krakatau, where it is strewn with other 

 jetsam of the sea along the drift-zone (PI. IV., fig. 3). 



All these different possibilities of transport over water, the com- 

 paratively short distance separating Krakatau from the coasts of 

 Java, Sumatra, and other plant-covered islands, and especially the 

 unusually favourable current-conditions have contributed to the 

 result that the germs of a large number of plant species have been 

 carried in a short time to the shores of Krakatau. The plants so 

 introduced include species with seeds which are not adapted, or 

 only in a slight degree, to dispersal by water. In addition to widely 

 distributed strand-plants the Krakatau strand-flora includes also less 

 well defined strand-species. 



The number of species of the strand-region (67) appears small in 

 comparison with the number included in the Indo-Malayan strand-flora 

 (ca. 320). Several typical and widely-spread members of the Pes-caprae 

 and Barringtonia formations are still unrepresented. We searched in 

 vain, for example, among the Spinifex bushes for Tacca pinnatijida, 

 with its beautiful foliage, which occurs in abundance on the island of 

 Edam. The handsome bushes of Crinum asiaticwn, which decorate 

 with their white flowers the Barringtonia forest, do not occur, nor the 

 tall Calotropis gigantea which in other places is a common plant on 

 sandy beaches. The latter is an Asclepiad with large violet flowers, 

 and seeds covered with long, shiny and silky hairs which distinguish it 

 as one of the few sea-shore plants adapted to wind-dispersal. Even 

 more noteworthy is the absence on the beach of Krakatau of the 

 whole Mangrove association which is so rich in species characterised 

 by morphological and ecological peculiarities. The absence of these 

 and other typical strand-plants is attributable to different causes. In 

 some cases the species do not occur, or only in small numbers, on the 

 stretches of coast which supplied most of the fruits drifted to Kra- 

 katau. Others may have reached the beach but failed to find the 

 requisite conditions on the pumiceous and ash-streAvn ground. The 

 fruits and seeds which we found most frequently in the drift-zone of 

 Krakatau and Verlaten island are those mentioned in the lists given 

 by Treub and Penzig ; they are represented in the new strand-flora by 

 many individuals, some of which have already reached the fruiting 

 stage. Other plants drifted to the shore in considerable quantity 

 produce a few seedlings, which, however, as is the case of Nipa 

 fruticans and like the large seedlings of Rhizophora which are washed 

 up on to the beach, fail to develope further. The absence of certain 

 strand-plants like Nipa and the Mangrove plants, the seeds of 

 which reach the island but do not survive, is due to the special con- 

 ditions which prevail on the shore of the island. Another type of 



