75 



India air-temperatures of 50 52 C have been recorded. Massart 1 ) 

 saw in 1898 in the Sahara a rather rich vegetation of higher plants 

 on a soil heated to 67 C. Peschuel Loesche found on the 

 shore of Loango (West- Africa, + 5 southern latitude) a profus- 

 ely flowering Ipomoea on a sandy soil which, at its surface, had a 

 temperature of 69 C. Several lichens thrive on rocks which are regularly 

 heated up to 60 C, one species even on' rocks heated up to 70 C -). 

 Ernst - ! ), it is true, says of Krakatao: ,,Der Boden wird jeden Tag, 

 ,,ebenso auf hellen Tage der Regenzeit, auf Temperaturen erhitzt, 

 ,,welche das Warme-maximum fur Keimung und Wachstum der meisten 

 ,,Pflanzen bedeutend iibersteigen," but this assertion is not corroborated 

 by any experiment made by him in order to ascertain at which maximum- 

 temperature tropical plants can germinate, live and grow under such 

 circumstances as prevail on Krakatao. On this important point nothing 

 has been examined, much less proven. 



7. The ashes and pumice of Krakatao are almost everywhere 

 covered \vith a thin gelatinous hygroscopical layer of greenish or 

 glaucous algae (Cyanophyceae). Ireub does not doubt that only the 

 presence of this layer enables the spores of the ferns to germinate. 

 Hence the algae prepare the so/7 for the ferns about in the same 

 manner as these, in their turn, will do for the Phanerogams. 



This discovery of 1 r e u b is of real importance. Properly speaking 

 it is the only important result the botanical investigations of Krakatao 

 have yielded up to now. Probably, Cyanophyceae, which need only a 

 minimal quantity of soil-nitrogen, were spread throughout the island. 

 In September 1896 Burck, Boerlage and Mulder found 

 these algae also in another island of the Krakatao-group. Lang Eiland. 

 There they formed a thin layer on the ravine-walls shielding these 

 from being washed off by rainwater flowing dow (Cf. Chapter V) 

 Half a year afterwards P e n z i g '") and his companions saw such a 

 layer of algae in many spots in Krakatao; Ernst ) found it back 

 in 1906. 



Treub's supposition that the hygroscopical slimy layer of algae 

 strongly contributed to enable the spores of ferns and mosses to 

 germinate is probably correct- T r e u b found in a sample taken on 



!) Voyage Botanique au Sahara in Bull. Soc. Royale Bot. Belgique XXXVII (1898) 

 285. 



2 ) S c h i m p e r, Pflanzengeographie, 2e Auflage (1908), p. 49. 

 8 ) Neue Flora Vulkaninsel Krakatnu (1907), p. 50. 



4 ) Ann. |ard. Bot. Buitenzorg XVIII (1902), p. 101. 



5 ) Neue Flora Vulkaninsel Krakatau (1907), p. 32. 



