122 Principles of Plant Culture. 



188. The More Water Plant Tissues Contain, the 

 Sooner they Freeze. Since the water of plants is not 

 pure, but is a solution of various substances, it does 

 not freeze at the freezing point of pure water (32° F.), 

 but at a lower temparture, determined by the degree 

 of concentration of the solution, or the intimacy with 

 which it is combined with the tissues of the plant. The 

 more thoroughly dormant the condition of a plant, or 

 part of a plant, the less water does it contain, and the 

 better is it able to endure cold (174). 



189. The Power of Plants to Endure Cold depends 

 upon various conditions, aside from the amount of 

 water contained, as 



a— Heredity. Plants by nature possess widely differ- 

 ing powers to endure cold. The Anoectochilus (a-ncec'- 

 to-chi'-lus) perishes when exposed for a considerable 

 time to a temperature of 42°. F., while other plants, as 

 the common chickweed,* are uninjured by prolonged 

 cold, far below the freezing point (175). 



h—The rate of thaiving of the frozen tissues. The 

 more slowly the thawing takes place, the less likely is 

 the frozen part to suffer injury. Many bulbs, tubers 

 and roots which survive the severest winters within the 

 soil, where they thaw slowly, are destroyed by moderate 

 freezing if quickly thawed. Frost-bitten plants are sel- 

 dom injured when sheltered from the morning sun by 

 a dense fog, which causes them to thaw slowly. Apples, 

 covered in the orchard in autumn by leaves, sometimes 

 pass a severe winter with little harm. 



* Stellaria media. 



