48 



PRACTICAL TREE REPAIR 



pass, unless a series of mild years permits them 

 to grow together. The cracks are caused by sud- 

 den cold snaps which very suddenly freeze the 

 outer layers of the sapwood while the heartwood 

 is still comparatively warm on account, frequently, 

 of its connection with the lower and warmer parts 

 of the soil through the taproot of the tree. 

 Freezing a wood cell draws the water out of the 

 cell wall and collects it in a crystal in the center 

 of the cell. When this happens the cell wall has 

 to contract. If, in a cold snap, the periphery of 

 the trunk contracts suddenly, before the inner part 

 has time to cool and contract proportionately, 

 something has to give way, and a 

 frost crack is the result. After the 

 crack is once formed sap flows into 

 it, and, freezing, enlarges and per- 

 petuates the opening. Bark pres- 

 sure being removed from the con- 

 tiguous cambium, it is stimulated to 

 greater than ordinary growth and 

 soon develops " lips." Frost cracks 

 should be attended to promptly, for 

 they are frequent sources of infec- 

 tion. If the injury is discovered 

 soon after it occurs, the crack should be painted 

 with liquid grafting wax, and if possible filled 

 with grafting wax or cotton batting dipped in hot 

 tar or asphalt. When calluses form their union 



Cross-section 

 through three- 

 year-old frost- 

 crack 



