229 



see p. 187. The 7 ,grassy wilds", as a whole, are not level but 

 slope upwards towards the interior of the island, as may be seen 

 from the picture given by Mr. Docters van Leeuwen 1) himself. 

 In 1908 they covered very many of the ridges. If in 1919 they really 

 only ,,occasionally rose to them", why then did Mr. Docters 

 van Leeuwen not tell us with which other plants these ridges 

 were clothed in that year? One wishes Mr. Docters van Leeuwen 

 had told which trees, besides the few mentioned ones, were com- 

 ponents of the groves in the grass-jungle. Those found in 1908 are 

 recorded in Chapter IX. Now it is impossible to make a comparison 

 between the finds of 1919 and those of 1908. 



As it is not at all proven that on the south-eastern side and on 

 the top of Krakatao there ever existed a fern-zone, the ferns found 

 on the summit need not be considered as remains of this quite 

 hypothetical belt. Finally it should be stated that in Java Cyrtandra 

 sulcata Bl. is not a small forest-plant but a rather robust shrub, 

 often of 1 '/2 t 3 m. high. 



16 I lie two main problems to be solved in studying tlie new fiord of the totally 

 devastated islands of the Krakatao-group are, firstly: In what manner did the 

 plants yet there? and secondly: In what way was the soil made suitable to 

 yield a sufficiency of food to the plants? The researches on the second of 

 these problems have been very inadequate and now it is too late: for a long 

 time the ground has ceased being sterile as it was shortly after the eruption. 

 Volcanic matter will mostly weather readily, especially when this is furthered by 

 the action of lower organisms. From the analyses of ashes and pumice made 

 by W inkier and published by Verbeek, appeared that nearly all the 

 elements were present, except nitrogen. On the beach this could be disengaged 

 from organic matter washed ashore. Nitrogen-containing acids were brought 

 to the soil in rain-water. De Kruyff found nitrogen-binding bacteria in the 

 soil-samples brought back by Ernst. Algae, bacteria and moulds play their 

 parts in this process, being organisms which, like the Cyanopliyceae found by 

 Ireub, are extremely sober in their requirements of nutriment. These little 

 plants by their growth cause the surface-soil to crumble and moulder more 

 easily and furthermore, when they die and decay, small amounts of organic 

 matter enter the soil, which are transformed again by other micro-organisms. 

 Eventually such soils will sustain a few frugal plants. On the beach the usual 

 littoral plants found what was sufficient for them in the way of nutrition; 

 typical representatives of this formation throve here after a short time and 

 this contributed to enable other plants start living a few years later, a little 

 more in the interior'-). These were mainly ferns, the same kinds as content 

 themselves in other places also with dry, slightly weathered soils. The begin- 

 ning therefore was principally the transportation of such soil-organisms as are 



!) Ann. lard. Bot. Buitenzorg XXXI (1921), tab XIX, beneath. 



'-) The Dutch text has here quite another reading, viz.: ,,en bovendien konden na 

 ,,enkele iaren in het binnenland andere planten komen", i.e. ,,and moreover, after a few 

 ,,years, other plants could arrive in the interior". 



