122 Principles of Plant Culture. 



Other chemical changes resiilt from cold, as the sweet- 

 ening of potato tubers when chilled, the removal of as- 

 tringcncy from the wild grape and persimmon, and the 

 heightening of the flavor of the parsnip. 



194. Tree Trunks are sometimes Split Open by Severe 

 Freezing, the split remaining open until the return of 

 mild weather. This most often occurs in hard-wooded, 

 deep-rooted, deciduous trees, as the oak, and appears to 

 result from the more rapid contraction of the outer 

 layers of the wood in a sudden fall of temperature. The 

 rents are usually overgrown by the next annual wood 

 layer (71). 



The splitting down of the main branches of certain 

 varieties of the apple tree appears to be favored by the 

 expansive force of ice in narrow crotches, which retain 

 snow and water. Varieties the branches of which leave 

 the trunk at a wide angle are not subject to this trouble. 



195. Bark-Bursting on the trunks of young apple ti'ees 

 often occurs w hen freezing weather overtakes late-grow- 

 ing and hence poorly-matured wood. In severe cases, 

 the bark splits longitudinally clear through the cambium 

 layer and from the ground to the lower branches; and 

 the bark is loosened from the wood nearly or quite 

 around the trunk. Such trees are practically ruined, 

 but trees slightly injured by bark-bursting may fully 

 recover. 



Bark-bursting is usually most severe on deep, rich, 

 moist soil and in seasons that favor late growth, or in 

 which freezing weather occurs unusually early. Late- 

 growing varieties are most subject to it. Its occurrence 

 is lessened by treatment that favors early maturity of the 

 wood (200, 201). 



