80 



the same conditions prevail as in Krakatao. And so little is 

 known of the vegetation of Krakatao in the first years after the 

 eruption that a reliable comparison with other islands cannot be 

 made, supposing the vegetation of these latter to be sufficiently 

 known. 



The predominance of ferns in the locality investigated by T r e u b 

 is ascribed by him to the supposed fact that these plants are phys- 

 iologically less differentiated than Phanerogams. By this expression 

 he apparently meant to say that all ferns lay about the same claims 

 on their substratum and environment. 1 aken in this wide sense T r e u b's 

 thesis is undoubtedly wrong. In the tropics one finds among the ferns as 

 well as among the higher plants terrestrial and epiphytical, halophobous 

 and halophilous, heliophilous and heliophobous species. There are spe- 

 cies which require a very moist substratum and species which prefer an 

 only moderately moist one, species thriving only in soil rich in humus 

 and species growing in humus-deficient soils. It is true that very 

 many ferns do not require a fertile soil, that many are even typical 

 kremnophytes. I lence such ferns could be numerous in the sterile 

 locality investigated by I reub where Penzig II years afterwards 

 found the vegetation practically unchanged. By the same cause the 

 moist, higher parts of Ascension can bear a carpet of ferns. That 

 certain ferns can predominate in unfertile, not too dry islands is caused 

 partly by the modest claims they lay on the fertility of the soil, 

 partly by their easy and rapid reproduction by stolons or spores, which 

 are often formed in great quantities. Both of these factors are of 

 immense value in the struggle for life. Among the Phanerogams 

 occurring in the less dry regions of the Dutch Indies comparatively 

 fewer kremnophytes are found and these often have less simple means 

 of reproduction. When a new vegetation develops in a sterile con- 

 stantly humid locality, the Phanerogams, therefore, at first may form 

 only a small minority. Their number will increase as soon as the locality 

 begins to offer favorable conditions for their growth and reproduction. 

 Where these favorable conditions fail to come, the Phanerogams are 

 unable to supersede the vegetation of Cryptogams which are better 

 equipped for the struggle for life, and the succession predicted by 

 Treub will never take place. 



When we now proceed to sum up which reliable answers Treub's 

 investigations have given to the questions put in the beginning of 

 the Introduction, we arrive at the following conclusions: 



