67 



No. 13 and 19 of T r e u b's list, Stenoch/aena palustris Bedd. and 

 Acrostichum aureum L., ferns of humid or swampy localities, could find 

 suitable habitats in humid parts of the lower ravines, the last-named 

 fern especially in such places where, after the eruption, NaCI was 

 deposited by water oozing out (see p. 50, footnote 3). 



Of No. 18, the calcifugous Pteridium aquJlinum Ku/w, the very 

 poor specimen collected by Treub bore in 1924 on its rhizome 

 still vestiges of grey volcanic ashes. If these did not adhere to it 

 by some accident one would conclude from their presence that 

 Treub collected the plant on a field of ashes. The young ashes of 

 Krakatao offered to this species probably a rather unfit substratum 

 because of their high CaO-percentage. 



For No. 16, P ten's tripartite S\\'., a halophobous, non-kremno- 

 phytic, shallowly rooting fern of sunny or slightly shadowed, con- 

 stantly humid localities, the lower parts of Krakatao were in 1886, 

 as a whole, rather unfit; the pumice-covered ridges because of the 

 very porous upper layers of the soil becoming too dry after a few 

 rainless days, the bottom of the ravines because of the local deposits 

 of NaCI, But, in some places at least the locality must have been 

 favorable to its growth, the young specimen collected by Treub 

 being rather robust. One should bear in mind that Treub made his 

 collection in June or July, shortly after the end of the rainy monsoon. 



Summarizing, the investigated part of the island offered to 9 out 

 of the I I species in many localities favorable conditions of growth; 

 hence these 9 species may have occurred in great numbers. All of 

 them were found back in 1897 by Penzig or Raciborski. 



Treub takes for granted that the spores of the ferns found by 

 him were carried over from the surrounding islands to Krakatao by 

 wind. This he does not wonder at, for he believes that the much 

 heavier seeds or fruits of the Phanerogams were introduced in the same 

 manner. 1 argued already (p. 65) that this last mentioned supposition 

 is not in the least proven and though I fully admit for very light 

 and fine fern-spores the possibility of transport by wind over rather 

 large distances over land, I emphasize that in the case of Krakatao 

 it is not proven that direct transport of spores by wind from outside 

 the island, i.e. over a distance of at least 20 km. across the sea, has 

 really taken place. 



Without taking the wind, the water (p. 65) or man (pp. 10 and 33) 

 for the agent of introduction, the occurrence of many species of ferns 



