UNFAVORABLE TEMPERATUHE 115 



Gardeners harden plants grown under glass, by gradually 

 exposing them to the cooler out-door atmosphere, before 

 removing them to the open ground. 



The treatment of the frozen tissues. — Handling plants, 

 fruits or vegetables while frozen greatly aggravates the 

 damage from frost, probably because the handling in- 

 creases laceration of the cells by the ice crystals within 

 them. 



190. Treatment of frost-injured plant tissues. — Frost- 

 injured plants, fruits or roots may often be saved from 

 serious damage, if promptly placed under conditions that 

 cause the slowest possible thawing of the tissues, as shading 

 from the sun's rays, immersing in ice water or covering 

 with snow. They should be handled as little and as care- 

 fully as possible while frozen. Sprinkling with cold water 

 is often sufficient to restore frost-bitten plants. 



Aside from the death of tender plants by cold, more or 

 less hardy species suffer injury in a variety of ways, of 

 which the following are examples : 



191. Destruction of terminal buds by cold. — In 

 plants which do not mature their terminal buds in autumn, 

 as the raspberry, sumac, grape and the like, destruction 

 of the tips of growing shoots by frost is a regular occurrence 

 in climates of severe winters. The distance which the 

 shoots are killed back depends upon the succulency of the 

 growth, the severity of the winter and the natural power 

 of the plant to endure cold. Plants thus affected are not 

 always to be regarded as tender, since they often grow wild 

 in climates of very severe winters. 



192. The darkening of the wood (black-heart) of 

 certain trees, as the pear, in climates of severe winters, 

 appears to be a chemical effect of the cold. It begins at 

 the center of the stem and in extreme cases may extend 



