II4 Principles of Plant Culture. 
temperature, 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 7s it able to endure cold. 
190. 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 differing 
powers to endure cold. The Anectochilus (a-ncec’-to-chi’-lus) 
perishes when exposed for a considerable time to a temp- 
erature of 42° F., while other plants, as the common chick- 
weed,* are uninjured by prolonged cold, far below the freez- 
ing point. 
b — The rate of thawing 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 seldom 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. 
When the water that is withdrawo from the tissues in the 
freezing process is gradually set free, by slow thawing, it 
may be absorbed by them again and little or no harm results. 
c— The length of time the tissues remain frozen. A compar- 
atively slight degree of frost, if prolonged, may act more 
injuriously than a severer degree of shorter duration. Pro- 
longed freezing is especially injurious when the frozen parts 
* Stellaria media. 
