PROTECTION FROM FROST. . 153 



lines, when the body is surrounded by air, may always be 

 reflected back upon the body from which they emanate by 

 the slightest covering placed at a short distance from them ; 

 while, on the other hand, if this slight covering be placed 

 close to the body, instead of reflecting back the heat it 

 will carry it off by conduction, that is, the heat will pass 

 off through the covering closely applied, and be radiated 

 from its surface." (Daniel.) Hence the covering or pro- 

 tection given is far more efficient if it enclose a stratum 

 of air without actually touching the plant. 



When , plants are actually frozen, in many cases they 

 may be saved if they can be thawed gradually without ex- 

 posure to the sun. To effect this, if coverings are applied 

 before sunrise, or the plants are sprinkled repeatedly with 

 water until the frost is extracted, they generally escape 

 without serious injury. If a frosty night is followed by a 

 cloudy or foggy morning, injury to plants need not be ap- 

 prehended. 



Fruit trees and vines in blossom, or with young fruit 

 set, are in some large districts so liable to suffer from late 

 spring frost, that fruit bearing, in the case of those first 

 to bloom, is the exception. The crop is lost perhaps two 

 years out of three. It is seldom in the most frosty locali- 

 ties that they are endangered more than two or three 

 nights in a season, all the fruit of the peach being rarely 

 killed until it begins to enlarge, and the blossom is on the 

 wane. Such trees are too large to admit of being cover- 

 ed. They can, however, be fully protected by smoke. Or- 

 dinary smoke in still, frosty nights, rises rapidly, and to 

 be of any service, it must settle over the trees in a mod- 

 erately dense cloud, acting as a screen and preventing 

 radiation. A heavy, damp smoke, not rising rapidly, in 

 which the trees are kept fully enveloped until some time 

 after sunrise, is what is necessary to protect a fruit garden. 

 A slight frost will do fruit blossoms little injury, and there 

 are some, which, like those of the Forelle pear, will bear a 



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