230 



wont to effect the chemical transformation in the earth, which were succeeded 

 first by ferns and beach-plants and next after by grasses that are organized 

 to live on dry exposed soils, such as Saccharum spontaneum L. and //operate 

 cylindrica P.B. By their agency the amount of organic substance was gradually 

 added to, rendering the soil increasingly suitable for the growth of other plants. 

 In this connection it is remarkable that among the pioneers were the orchids 

 Spathoglottis plicata HI. and Arundina spec/osa Bl. which in lava freguently grow 

 on dry, steep banks. Orchids are among those plants that live in symbiosis 

 with fungi in their roots; these fungi are often indispensable even to their 

 germination. Not only must the seeds of those orchids have got to Krakatao 

 in great numbers but also the fungi. A large number of tropical plants, not 

 only forest-plants but beach-plants as well, as Dr. Von Faber has told in 

 his lecture of Oct. 3d 1919, live in symbiosis with fungi. Therefore an abundant 

 microflora is necessary for the life of the higher plants. 'I he number of 

 bacteria per gramme of earth was in the samples brought by Ernst from 

 Krakatao almost equal to that in the soil of Buitenzorg. Several Leguminosae 

 have been found with their nitrogen-tubercles; these plants help energetically 

 in rendering the soil fertile. 



Many plants could not grow on Krakatao before the humidity of the sur- 

 roundings had become greater. I his only became possible when the pioneers 

 of the arboreal flora, especially species of Ficus, had begun to build up forests 

 in the ravines. In these ravines watery vapours clung more easily and longer 

 tluin in the flat open ground; a layer of humus was formed, suitable to 

 smaller forest plants, the vegetation also becoming gradually so dense that 

 a moist shade prevailed beneath the trees, lust the thing for numerous 

 forest-plants, especially epiphytes. In this humus vegetate all kinds of fungi 

 preparing the conditions of life for higher saprophytes, that live in community 

 with fungi. Several orchids might be classed among these '). l.oranthaceae are 

 entirely absent. I his fact should be accounted for from the absence of the 

 birds that disseminate the Loranthus-secds, 



For a discussion of the contents of the first part of this para- 

 graph (for the greater part unavowedly borrowed from Ernst's 

 paper -'), I refer to p. 73. Herebefore I have already argued that it is 

 not proven, not even probable, that the soil of Krakatao was com- 

 pletely sterilized by the eruption of 1883. Contrariwise, as stated on 

 p. 74, an effect of the heating of the soil may have been a partial 

 sterilisation, causing an increased activity of nitrogen-fixing and nitrifi- 

 cation organisms. Like all his predecessors Mr. Docters van 

 Lee u wen forgets that the old woods covered by the eruptive prod- 

 ucts formed an enormous store of organic compounds. Wherever 

 the ashes and pumice were soon washed away or nearly so, the 

 organic material came on or near the surface again and could be- 



J ) The Dutch text adds here; ,,and probably also the species of Schizaca, a kind 

 ,,of fern belonging to the hemi-saprophytes". This statement is probably due to con- 

 fusion with Psilotum* I do not know that it has ever been proven that Sch. dichotoma 

 Sm. (the only species of the genus found till 1919 on Krakatao) lives in community with 

 fungi. Dr. Von Faber, the well-known Buitenzorg specialist to whom I applied for 

 information, kindly told me by letter that he knew nothing about the occurrence of a 

 fungus in Schizaea-roots. 



'-) Ernst, Neue Flora Vulkaninsel Krakatau (1907), pp. 51 seq. 



