120 AGRONOMY 



windbreaks, and cold frames. Mn1<-hin<i is simply adding to 

 the cover of dead leaves with which the ground is naturally 

 protected in winter. Any loose litter is good for this purpose. 

 Straw, leaves, and stable manure are the materials most fre- 

 quently used. In addition to protecting plants from being 

 heaved by the cold, a mulch retards the thawing of the ground 

 in spring and thus holds back early plants that might other- 

 wise be injured by late frosts. Windbreaks are belts of trees, 

 usually evergreens, planted on the windy side of gardens and 

 fields to protect them from the high winds of winter and early 

 spring. In nature the forest acts as a natural cover for a vast 

 number of plants. Cold frames are frames of wood covered 

 with glass or thin cloth, which are sometimes placed over 

 plants. They are either sunk in the ground to the level of the 

 soil, or are banked up with manure. On very cold nights they 

 are covered with mats as an additional protection. Sprinkling 

 plants with cold water may protect them from frost when the 

 temperature does not go much below the freezing point. In 

 orchard practice the blooming trees are often protected from 

 late spring frosts by smudge fires, which give off great quan- 

 tities of smoke that act like clouds in keeping the earth warm. 



Treatment of frostbitten plants. Plants that have been 

 frostbitten may often be saved by gradual thawing, especially 

 in cases where the injury is due to a withdrawal of moisture 

 from the cell. If possible, such plants should be removed at 

 once to a cool cellar, sprinkled with water, and kept out of 

 the direct rays of the sun for a few days. Out of doors the 

 plants may be sprinkled with water and protected from the 

 sunlight. Frostbitten plants and fruits should be handled as 

 little as possible until thawed. 



Effects of heat. The first noticeable effect of great heat 

 upon the plant is the wilting due to increased evaporation. 

 As the temperature rises, the plant is called upon for more 

 and more moisture until a point is reached where the demand 



