32 THE HARMONIES OF NATURE. 



of electrical discharges, they unite to larger drops, and fall to 

 the ground under the various forms of rain, snow, or hail. 



The rain-drops grow as they fall from a greater height, and 

 traverse the warmer and more humid atmospherical strata, 

 which are generally nearer to the surface of the ground. It 

 is a well-known fact that there is a considerable difference 

 in the quantity of rain falling within the same time upon 

 the summit of a hill, or at its foot, and thus the elevated 

 clouds, from which the rain originally descends, are merely 

 its starting-points. 



This gradually increasing weight of the rain-drops as they 

 fall is of great importance to vegetation. Had they at once at- 

 tained their full size at a considerable height, they would have 

 descended with terrific violence, and every shower of rain must 

 have been equal to a hail-storm in its destructive effects. So 

 much ground would also have been washed away from the hill- 

 slopes by these pelting floods, that large tracts of fertile country 

 must have been converted into naked wastes. 



In the tropical zone the rain indeed frequently falls in such 

 dense torrents as to produce a painful impression on the skin ; 

 but here the structure of the plants harmonises with the 

 meteorological character of the climate. Genera with thick 

 compact leathery leaves, which even the strongest rain cannot 

 damage, are prevalent; and such plants as have a more delicate 

 foliage mostly grow under the protecting canopy of the forest. 

 The glasses and cereals, such as maize and the sugar-cane, are 

 of a more robust growth than our indigenous species, and the 

 fruits generally ripen after the rainy season is past, or grow 

 under the shelter of a dense crown of leaves. 



The congelation of water at the comparatively moderate 

 temperature of + 32 F., when it either drops as snow from 

 the atmosphere, or covers the brooks and rivers with a sheet 

 of ice, is of immense importance to vegetation in the higher 

 latitudes ; for snow is so bad a conductor of heat, that under 

 its protecting mantle the plants of the Arctic regions are 

 able to resist the utmost rigours of the cold. Buried eight 

 or ten feet deep under its crystal pall, they pass the long 

 winter in a temperature not much below freezing point, while 

 without icy blasts capable of converting mercury into a solid 

 body howl over the naked wilderness. But for this protection, 



