HOW PLANTS ARE INFLUENCED 353 



The way in which a frozen plant is thawed out 

 makes a great difference. Allow some potatoes to freeze 

 (they may be easily frozen in a water-tight can, sub- 

 merged in a mixture of pounded ice and salt, or set in 

 an ordinary ice-cream freezer). Place some of the 

 frozen potatoes in water chilled by ice (but free from 

 salt) , and let them stand until the water reaches room 

 temperature. Place others at once in a warm place, so 

 that they will thaw quickly. 



Frozen leaves (and other plant- tissues) have a 

 peculiar transparent appearance on thawing ; the same 

 thing occurs when they are boiled in water or injected 

 with water in an air-pump (see page 190) ; in all these 

 cases it results from the air-spaces becoming filled 

 with water. It is supposed that when a plant is 

 allowed to thaw rapidly this water evaporates and that 

 the plant suffers injury, which might be avoided by 

 slow thawing, which would permit the cells to again 

 absorb the water which escapes from them into the 

 air spaces during the freezing. 



The action of frost on the trunk may result in long 

 splits in the trunk or in the killing of the ends of the 

 branches, which soon turn black. The best treatment 

 is to remove the injured portions by pruning and to 

 direct the energies of the tree to making new wood 

 (prevent it from bearing fruit for a season) to replace 

 that which is killed. 



Protection from frost is secured by covering the 



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