49 4 PROTECTION AGAINST FROST. 



sap do not freeze so readily as young wood and leaves, which 

 contain a more watery sap, and which, owing to the scarcity 

 of intercellular spaces in wood, turn to ice within the lumina 

 of the cell, at the same time depriving the cell-walls of their 

 water and causing them to shrink. 



Severe frost may thus impair the young zones of sap wood 

 in a tree without killing the cambium. The formation of 

 heartwood may thus he hindered and several zones remain 

 intermediate between sapwood and heartwood, forming a ring- 

 shake in the wood. Or the sapwood may be actually killed 

 and separated from the cambium, which continues the circum- 

 ferential growth of the wood outside the dead wood, so that 

 after the tree has been felled the inner portion may be found 

 completely separated from its outer zones by cup-shake. 



Molisch agrees with H. Miiller Thurgau in the theory that 

 Sachs' view that rapid thaw kills plants is not generally 

 correct. Hess, however, considers that the results of experi- 

 ence in vineyards and forest nurseries are strongly in favour of 

 Sachs' view, and also states that Thurgau has reconsidered 

 his opinion, and has shown that a frozen plant may be saved 

 by slow thawing, that would certainly be killed if thawed 

 rapidly.* 



3. Amount of Damage done. 



a. General Nature of Damage. 



Late and early frosts often kill young plants and destroy the 

 foliage, shoots, blossoms or young fruit of trees. This retards 

 their upward growth, causes a loss of increment and reduction 

 in quantity or complete loss of the crop of fruit; thus the 

 management may be impaired, especially when natural 

 regeneration is desired. Early frosts hinder the complete 

 ripening of the wood, especially in coppice-shoots; by the 

 early fall and killing of leaves forest trees suffer a loss in 

 potash and phosphoric acid, if these substances have not 

 completely returned to the stem, as they do before the normal 

 leaf-fall. Owing to the narrow annual zones of wood which 

 are formed in years of severe frost, they may be recognised on 



* Molisch, H., " Untersuchungen iiber das Erfrieren tier Pflan/.en." Jena, 

 1897. 



