79 



It is only fit for a kremnophytic vegetation. Whether this vegeta- 

 tion will consist of ferns or of other plants depends very much on 

 the degree of moisture: a fern-association thrives only in not too dry 

 localities. The mean annual temperature 1 ) of Ascension [29 30 C at 

 the coast, 24 C on the top (860 m.)| is very much higher than in |uan 

 Fernandez, the amount of rain, on the contrary, is much smaller: 

 it averages only 500 mm. a year. But there are years in which the 

 rainfall on the island - locally at least - is much less than 500 mm. 

 From 1863 till 1865 it averaged-) only 84 mm., distributed as follows: 



Jan. Febr. March April May June |uly Aug. Sept. Oct. Nov. Dec. 

 II 3 29 5 6 14 7 623. 



Perhaps the latter record bears on another locality than the first. 

 How this may be, it is certain that considering the nature of the soil, the 

 very high temperature, the comparatively small rainfall and the impossi- 

 bility of irrigation, the lower parts can bear only a meagre vegetation. 



But another situation presents itself in the higher parts of the 

 island. The top, popularly called Green Mountain, is very often wrapped 

 in clouds which bring moisture and hinder evaporation. Here rises 

 the only brook the island possesses, here such conditions are found 

 as favor a kremnophytic vegetation: humidity and an unfertile soil; 

 here the soil is clothed with a carpet of ferns. And here too does 

 not exist a shadow of a proof that the scarcity of higher plants is 

 due only to their seeds not being introduced. 



Treub might have cited other instances of isolated islands, 

 as St. Helena, the Canaries, the Hawaiian Islands. But all of these, 

 bearing a rich vegetation of Phanerogams, disprove his hypothesis 

 which therefore has to be rejected. 



9- When a new flora develops on a volcanic island \vhich is in 

 the same circumstances as Krakatao, the Phanerogams a/ways will be 

 preceded by Cryptogams because the latter, physiologically spoken, 

 are less differentiated. In such-like localities the vascular cryptogams 

 and especially the ferns, perform at present still the part they per- 

 formed very often in earlier times, when they constituted the main 

 vegetation of the earth. 



This conclusion too is rather vague. For there is no other island 

 where as to climate, soil, environment and further circumstances, 



!) Cf. Encyclopaedia Britannica, llth Ed. II (1010) p. 710. WinHer Prins, 

 Geillustreerde Encyclopaedic II (1015), p. 103. 



'*) These data on the rainfall received by courtesy of Dr. V i s s e r, subdirector 

 of the Royal Magn. Meteor. Observ. Batavia. 



