ENEMIES AND DIFFICULTIES OVERCOME. 81 



Upon some meadows, the fruit-buds in spring, or unripe 

 berries in autumn, are destroyed by frost, while others in 

 the same neighborhood escape uninjured. Natural bogs 

 are more apt to suffer from this cause than those which 

 have been sanded. This is partially owing to the dense 

 covering of sphagnum, bushes, etc., keeping the swamp 

 from becoming warmed during the day. In all cases 

 where the soil is barren, deprived of vegetable growths, 

 stony, or sandy, it becomes far hotter by the absorption 

 of the sun's rays, and hence less liable to frosts than one 

 that is covered with plants ; for instance, in the deserts 

 of Africa, the heat of the sand often amounts to from 

 122 to 140 F., while upon the oases, where the surface 

 is clothed in verdure, the temperature of the soil is always 

 lower. 



Plants cool much more rapidly by nocturnal radiation 

 than the earth, and this fact, in connection with their 

 being at a lower temperature at sundown, is sufficient to 

 explain why frost is deposited sooner upon vines growing 

 among mosses and grass than it is upon those cultivated 

 upon beds of sand. 



But even when the temperature is sufficiently low to 

 produce frost on cultivated meadows, the berries some- 

 times escape without injury. 



It is a peculiarity of frost that, when removed gradu- 

 ally, it loses its power to destroy. Even tender garden 

 plants, when frosted, may sometimes be saved by throw- 

 ing cold water on them early in the morning. 



When frost forms on vines in a swamp, it remains until 

 the rising sun dispels it rapidly, thus causing destruction 

 among the tender buds and green berries, while upon 

 some cultivated meadows, when a slight frost forms dur- 

 ing the night, the sand, by reason of its conducting power, 

 thaws it gradually, without any injury resulting there- 

 from. 



James A. Fen wick observes that "cranberries suffer 

 4* 



