46 MOISTURE AND ARBORESCENT GROWTHS. 



growths ; where the moisture is excessive, conditions 

 of soil being suitable, the tendency is to produce heavy 

 forest growths; where the rains are followed by a long 

 dry period, the tendency is to produce stunted trees, 

 or bush and jungle; where the winds are dry, and the 

 rains variable, the tendency is to produce treeless 

 plains with herbage only; where winds are dry and 

 rains wanting, a desert of course occurs. Such in 

 brief are the principal conditions which operate, as we 

 humbly venture to assert, to create the great system 

 of climatic zones. It may, however, be objected that 

 the division of these zones is really a botanical rather 

 than a climatic one : that is so to a great extent, be- 

 cause the truest test of climate is vegetation. 



Tell a botanist what plants grow in a given district, 

 and he will tell you what its climate and mean tem- 

 perature should be, and whether it has a dry or a 

 moisture-laden atmosphere. Let us take the cocoa-nut 

 (Cocos Nuciferd) as an example. If this tree grew 

 there, the climate must have been equatorial, the 

 atmosphere was hot, moist and equable, and the ele- 

 vation above sea-level did not exceed 2000 feet: that 

 being so the locality was probably near the sea board, 

 because the cocoa-nut is a sea-loving plant, very 

 sensitive to changes of temperature, so that on the 

 inland highlands where the temperature is subject to 

 variations, the tree could not survive. Or again, take 

 the date palm (Phoenix Dactyliferd); if that tree was 

 found there, it was the Desert Zone, with an extremely 

 dry atmosphere, with powerful suns, and an almost 

 rainless climate; but the subsoil contained water, and 

 a pit sunk near its foot would have found water, 

 perhaps of a brackish or salinous quality, but still 



