n] FEATURES OF ENVIRONMENT 19 



80 inches for a 'rain-forest/ the more the better. 

 This rain must be distributed rather evenly, that 

 is, seasons of drought must not be too prolonged. 

 The dry period, if there is one at all, must not 

 amount to more than three months, lest there be a 

 standstill of the vegetation, causing deciduous leaves 

 and other great changes in the general aspect. 



An annual rainfall of 80 inches is, in itself, not 

 terrific. For comparison it may be stated that we call 

 a climate with half this amount decidedly wet. The 

 North-West of Scotland and the wettest parts of 

 Ireland enjoy about 60 inches, but in the tropics 

 the rain makes itself more impressive by frequent 

 thunderstorms and by falling within a few hours of the 

 day. A fall of half an inch if spread over the twenty - 

 four hours, makes with us a very wet day. A fall 

 of an inch during a few hours' storm is of common 

 occurrence in the tropics, and the mere mechanical 

 effect of such a mass of falling water upon animals 

 and plants is considerable. The electric discharges 

 which accompany these torrential storms produce a 

 great amount of nitric acid which is washed out of 

 the air into the humus, and this process contributes 

 much to the wonderful exuberance of the vegetation 

 in every tropical rainy district. 



There are three large regions in the world, which 

 fulfil these conditions. 



First : Tropical America, with the huge basin of 



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