Plants as Affected ~by Cold. 123 



When the water that is withdrawn from the tissues 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. 



GThe length of time the tissues remain frozen. A 

 comparatively slight degree of frost, if prolonged, may 

 act more injuriously than a severer degree of shorter 

 duration. Prolonged freezing is especially injurious 

 when the frozen parts are subjected to drying wind, 

 which evaporates their water, while the frozen condi- 

 tion prevents movements of their fluids. 



dThe frequency with which freezing and thawing 

 are repeated. Frequent slight freezing and thawing 

 are far more injurious than a prolonged frozen condi- 

 tion, even though the latter occurs at a much lower tem- 

 perature. Winter wheat and rye, and strawberry beds 

 are often more damaged in mild winters, in which freez- 

 ing and thawing weather alternate, than in more severe 

 ones, when the temperature is mostly below freezing. 

 The chief damage is usually dene to these crops in late 

 autumn and early spring. 



QThe previous treatment of the plant. Plants grown 

 by artificial heat may be far less able to endure cold 

 than others of the same varieties grown in the open air, 

 possibly owing to the more succulent condition of the 

 former. Gardeners harden plants grown under glass, 

 by gradually exposing them to the cooler out-door at- 

 mosphere, before removing them to the open ground. 



iThe treatment of the frozen tissues. Handling 

 plants, fruits or vegetables while frozen greatly aggra- 

 vates the damage from frost, probably because the han- 



