126 



Wherever the investigated localities had been covered in 1883 

 with a thick and permanent layer of ashes and pumice they 

 doubtless received a new flora after that year, but it is unknown 

 whether this flora originated from outside the island or from the 

 washed-off parts where the original soil had come to the surface 

 again. It is certain that the secondary vegetation in the investigated 

 parts was thin in 1886, locally much denser in 1897. Quite analogous 

 phenomena may be observed in not too dry regions of Java. There 

 also the secondary vegetation begins with a thin vegetation of 

 grasses soon becoming denser and often intermixed with ferns; on 

 this point the investigation of Krakatao has disclosed nothing that 

 was not already known long before from elsewhere. But the real 

 problem: ,,has indeed the new flora of Krakatao entirely been intro- 

 duced from elsewhere and, if so, in wich manner?", has remained 

 completely unsolved even unattacked by the explorations of Treub 

 and Penzig. It is quite conceivable that in steep rocky localities 

 deficient in humus the kremnophytic vegetation predominated in 1897 

 as it did in 1886; probably that vegetation will maintain its character 

 for years. 



It is very improbable that the lack of forest in the investigated 

 parts of Krakatao was exclusively or mainly due to unfertility of the 

 soil. It does not appear that Penzig has instituted any investiga- 

 tion on this point. On the mere strength of T r e u b's assertion of 

 1886 he has taken the unfertility for a proven fact. Soils fit for a 

 luxuriant Sacc/jany/H-vegetation are in a tropical region receiving so 

 much rain as Krakatao sufficiently fertile for the development of 

 forest. But, if forest is to develop, two conditions have to be ful- 

 filled, viz. sufficient import of seeds fit to germinate and enough 

 time for them to develop into trees. Hence we have to ask : Had 

 the investigated localities long enough before 1897 received an 

 amount of seeds sufficient to permit the development of forest. 



In my opinion this was not the case. Though I fully admit the 

 possibility that seeds of inland plants in some way or other were 

 imported from elsewhere, I believe that this import did not taken 

 place on a large scale or, at least, that not many of the seeds im- 

 ported found a locality fit to germinate in and to develop further. The 

 revegetation of the interior of the island had in my opinion in the 

 first years to originate mainly from seeds or spores produced 

 on the island itself. In the higher ravines on the east-, south-east- 

 and south-side, where the original soil soon was laid bare, the forest 



