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10 were found back in 1897; Penzig and his companions collected 

 only 3 ferns or fern-allies not found by Treub. If one assumes that 

 all these ferns were introduced from outside the island after the 

 eruption it is singular that within the 3 years elapsed between the 

 eruption and Treub's visit no less than 11 ferns were introduced in 

 the examined locality; contrariwise but 3 ferns or fern-allies in the 



1 1 years elapsed between T r e u b's visit and that of Penzig. 

 If, on the contrary, we assume that most or all of the ferns found by 

 Treub had inhabited before the eruption the basaltic slopes or the 

 higher ravines (see pp. 66 69) and that a number of specimens had 

 escaped destruction by means of spores or rhizomes, consequently 

 that but very few species had to be introduced form outside the 

 island, the extraordinary concordance between the fern-flora of 1886 

 and that of 1897 is quite naturally explained. 



For the first time were in 1897 found 3 species, viz. Drynar/a 

 quercifolia, a fern which usually lives on trees but frequently also on 

 rocks or on steep walls, Ophiog/ossum reticu/atum L., a rather com- 

 mon fern of badly pervious or very stony soils and the club-moss 

 Lycopodium cernuum L., one of the commonest kremnophytes of Java. 

 These 3 species also may long before the eruption have lived in 

 unfertile localities or on steep walls near Zwarte Hoek and may have 

 survived the catastrophe. Treub's investigation in 1886 of the very 

 accidented locality must necessarily have been very cursory and 

 several species may have been present that he did not see. Penzig 

 himself admits that even in 1897, when 5 botanists and a very able 

 native plant-collector examined the locality, species may have been 

 overlooked. Moreover, one should always bear in mind that in 1886 as 

 well as in 1897 only a small part of the island was examined and this 

 only hastily; consequently that when a species was not found this 

 by no means furnishes proof that it did not occur. Therefore we have 

 no right to take for granted that the 3 species not found by Treub 

 in 1886 were introduced after that year. It is not even certain 

 that they were introduced at all after the eruption; they may have 

 survived it. Of course I will not deny the possibility that after 1883 

 a number of plants were introduced. For the halophytes and the 

 typical littoral plants this is next to certain, as the original beach 

 of Krakatao partly was destroyed by the eruption, partly was per- 

 manently and deeply buried, and it is not probable that the interior, 

 before the eruption, offered any fit habitat to halophytes or typical 

 littoral plants. These are the following: Acrostichum aureum L.,- 



