74 



organisms still remained in the soil. The sole effect of the eruption 

 and the heating of the soil should be a partial sterilisation, the effect 

 of which is an increased activity of the nitrogen-fixing and nitrification 

 organisms. 



The glowing heat on Krakatao is rather exaggerated by Treub, 

 who, living usually an indoor-life, was no trained mountaineer and did 

 not possess great physical force, He visited Krakatao in June or July, 

 in the beginning of the east-monsoon, apparently on a sunny day, and 

 must -as all untrained walkers in the tropics -when ascending the 

 shadowless steep slopes have suffered much from fatigue and thirst. 

 Hence he got the erroneous impression of the locality being contin- 

 ually heated by a burning sun. But in the west-monsoon the sky is 

 often cloudy for days, even for weeks, and there falls very much 

 rain. In that season there is no question of the soil drying out, the 

 air is very humid and the fern-spores can easily germinate. Dew 

 also brings water and, by its evaporation, coolness. When the roots 

 of the young plants have grown to a certain length they can absorb 

 sufficient water from the soil, only the upper layer of which dries 

 much out in the east-monsoon. This monsoon is, moreover, frequently 

 interrupted by rain-days. In the tropics many plants may be seen 

 thriving on a hot and apparently very dry soil. On the glowing sand 

 of the dunes of Madura ') I found in |uly 1916 after a drought-period 

 of many weeks, several quite fresh seedlings of Tribulus cistoides L. 

 On rocks and sand it may be frequently observed that plants can 

 stand very high soil-temperatures; besides, only the upper layers 

 of the soil are so strongly heated. Not the heat, but the drought 

 caused by long rainless periods finally kills the plants. Man, always 

 inclined to an anthropocentrical trend of thought and often insuf- 

 ficiently trained in bodily exercise, often measures heat by the 

 trouble it causes him. Fatigue and thirst are apt to confuse the 

 observations frequently made without instruments. A really very high 

 soil-temperature is in West-Java a very rare phenomenon. In one of 

 the islands of the Krakatao-group, Lang Eiland, the temperature, 

 from which the observer -) suffered much, amounted in a sheltered 

 locally only to 34 C and fell during the night to 30 C; the tem- 

 perature of the soil heated by the direct action of the sun rose in 

 the afternoon but little above 60 C. For tropical and subtropical 

 plants this is by no means an extremely high temperature. In British 



!) Cf p. 72, footnote 1. 



2 ) Tijdschrift Kon. Nederl. Aardrijksk. Genootschap XIV (1897), p. 120. 



