Pioneers of Vegetation 49 



ripening of its fruits. Anemophilous plants which have obtained 

 a footing on the ground will presumably produce a large crop of 

 fruit and thus be in a better position, from the point of view of dispersal 

 over the virgin soil, as compared with others with special contrivances 

 for the pollination of their flowers by particular insects which are un- 

 likely to exist on a newly formed and isolated land-area. For the 

 same reason dioecious species often fare badly in regard to dispersal. 

 If only a single individual of such a species occurs (as in the case of 

 Ci/cas on Krakatau), or if a few are spread over a wide area, the 

 production of fruit is clearly impossible. Plants of this class will 

 therefore cease to form a part of the flora if new seeds, capable of 

 germinating and producing individuals of the opposite sex, do not 

 reach the island before the death of the first arrival. 



During the first few years of the colonisation of Krakatau the 

 injurious influences of intense insolation and of running water must 

 have acted as a serious check to the pioneers of vegetation on the 

 fields of pumice and volcanic ash. There is comparatively little rain 

 in the dry season of the year which, presumably at Krakatau, as at 

 Batavia and other places on the north-west coast of Java, continues 

 with the south-east monsoon approximately from May to September. 

 Every day, also on clear days in the rainy season, the temperature of 

 the ground considerably exceeds the maximum for the growth and ger- 

 mination of the majority of plants. The total rainfall of the island 1 

 probably amounts to 2| metres [98 inches] a year, the greater part 

 falling between December and March. The denuding force of the 

 streams after each heavy downpour of rain, more especially during the 

 first few years after the volcanic outburst, produced surface-changes 

 and many seeds must have been swept away with the loose superficial 

 rock ; many seedlings which had developed despite unfavourable 

 conditions must have been "torn up or buried in sediment. 



The chemical composition of the substratum and its physical 

 properties were, on the other hand, not so unfavourable to plant- 

 colonisation as one would expect. The analyses of the ash and 

 pumice made by C. Winkler and given by Verbeek (loc. tit. u. 

 p. 305) show that they contain a sufficient quantity of all the inorganic 

 salts necessary for a plant (excluding nitrogenous and phosphorus- 

 containing compounds) and, a fact of primary importance in plant-life, 

 the salts occur, in part at least, in a soluble form. The following results 



1 In West Java the average from 24 stations is 276 cm., in East Sumatra the 

 average of 10 stations is 264 cm. ; for the whole Archipelago the mean rainfall may 

 be reckoned at 252 cm. 



s. 4 



