68 Formation of Plant-Associations 



borne species constitute 37 / (25 phanerogamous plants, 16 ferns) of 

 the vascular plants. The large number of Ferns and other cryptogams 

 is obviously explained by the fact that the prevailing winds in this 

 region serve for the dispersal of germs over a distance of approximately 

 30 kilometres [18^ miles], while as regards more distant islands the 

 transport of even the lightest germs is effected only by unusually high 

 winds and is therefore of comparatively rare occurrence. This is in 

 accordance with the remarkable fact that in the Cocos islands, which 

 have several phanerogams in common with Krakatau, Ferns are entirely 

 absent and only three cryptogams, a moss {Hypnum fuscens, Hook, 

 and Am.), a fungus (Polyporus luridus, Fries), and a lichen are re- 

 corded by the three naturalists Darwin, Forbes, and Guppy who 

 have visited the islands. 



VI. The succession of plant-associations and the future 

 character of the vegetation of Krakatau. 



The comparatively advanced state of differentiation of the vegeta- 

 tion into plant-associations or formations is no less surprising than 

 the remarkably large number and the variety of species in the new 

 flora of Krakatau. As Penzig showed, the development of plant- 

 associations had already begun in 1897. On the beach the plants of 

 the Pes-caprae formation predominated. In the interior of the 

 island the vegetation presented the appearance of a grass-steppe. 

 Ferns constituted the dominant plants on the slopes of the cone. 

 Since 1897 the aspect of the vegetation has undergone considerable 

 change ; the strand-flora is divided into two formations. An outer 

 zone of varying breadth, reaching in places to the tide-level, consists 

 of low creeping grasses and herbaceous plants, bushes and shrubs; 

 the typical Pes-caprae formation. Behind this rises the strand- 

 forest (Barringtonia formation), the composition of which is not 

 yet equal in variety of species and in gloomy grandeur to the 

 Barringtonia strand-forests on the coasts of Java and Sumatra, 

 nor will it soon reach the same level. Neither of these strand- 

 formations is as yet closed. Grasses, Cyperaceae, Ferns and 

 Composites spread from the grass-steppe of the interior through 

 clearings in the forest to the lower carpet of Ipomaea and Spinifex, 

 while in other directions groups of strand-plants have penetrated 

 inland for a distance of 300 500 metres. The beautiful group of 

 coconut palms, 400 metres from the shore-line, represented in the 

 photograph (PL VI., fig. 7, p. 30), affords an example of the latter. 

 Groups of older plants of Barringtonia, Calophyllum, and Casuarina 

 occur at various distances from the shore, while others, young coconut 

 palms and Pandanus clumps, are so near the edge of the sea that their 



