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exposed parts of plants freeze, if struck by sudden strong sunshine. The 

 cell contents, suddenly struck in a condition of rigidity, the result of cold, 

 are found poor in water content and drawn back from the cell wall, and do 

 not have time to distend again, by absorbing water, into their normal rela- 

 tion with the cell wall, and, thereby, the surrounding tissues. In this way, 

 the disorganization of the cell begins. These arc the processes which occur 

 with spring frost and are especially advantageous for garden plants. 



(b) The Use of Water. 



Especially herbaceous plants which are suddenly exposed to frost are 

 benefited if the hard frozen parts of the plants are watered with right cold 

 water and then shaded. The water on the plants freezes to an ice crust, 

 thus raising slowly the temperature of the plant itself to zero, and it can 

 gradually be warmed further above this temperature, after the thawing of 

 the crust. 



On the same principle of gradual warming rests the plunging of frozen 

 potatoes and roots into a vat full of cold water and the piling of frozen 

 cabbage heads in heaps which are then covered with straw mats. 



In spring and autumn, when the air temperature does not fall to zero 

 but the plants, because of their radiation of heat under a bright sky, cool 

 down below zero, become covered with frost and freeze, they may be pro- 

 tected by substances arresting radiation. Covers and mats are spread over 

 the plants, also very thin cloths are effective here and, if no other covering 

 material is at hand, a thin layer of brush is very useful; even perpendicular 

 walls have proved excellent protection against frost. They are effective, 

 on the one hand, by keeping off the wind and, on the other, by decreasing 

 radiation from the plants. In trees, trained against stone or wooden walls, 

 in addition to the very considerable decrease in radiation of the trees on the 

 side next the wall, the wall itself gradually gives up its stored heat to the 

 benefit of the trees. 



A less effective, but not entirely rejectable, protection against frost is 

 recommended by ®lder authors and is practical in gardens in spring. The 

 trunks of trees are wound with straw rope one end of which dips into water. 

 Straw and tow ropes are suspended in all directions over beds of blooming 

 spring plants some distance above the surface of the soil, their ends being 

 held fast by stones in a vessel filled with water. 



To understand the favorable effect of this process, one should remem- 

 ber the great latent warmth in the water. If the water in the saturated 

 straw ropes freezes, heat is set free which is advantageous, since it prevents 

 the penetration of the cold to the underlying parts of the plants. Thus 

 plants, near larger bodies of water, freeze less easily. One measure used 

 with good results for potted plants, at a time when night frost may be 

 feared, consists in a decreased watering, whereby the tissue of the plant 



