VNFAVOBABLE TEMPERATURE 117 



194. Bark-bursting on the trunks of young apple 

 trees often occurs when freezing weather overtakes late- 

 growing and hence poorly-matured wood. In severe cases 

 the bark splits longitudinally entirely through the cambium 

 layer and from the ground to the lower branches ; and the 

 bark is loosened from the ^^'ood 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 more 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 (199, 200). 



195. Root-killing of trees. — When a very dry autumn 

 passes to winter without rain or snow, the surface layers 

 of the soil sometimes freeze so severely as to destroy the 

 roots of trees. Root-killing is usually most serious on 

 light soils, and on one-year-old, root-grafted (391) nursery 

 trees (.386). With very severe freezing on bare ground, 

 root-killing sometimes occurs on soil well supplied with 

 water. The destruction of the roots may be complete or 

 only partial. In the latter case, the tree, if of a vigorous 

 variety, may largely outgrow the trouble, though complete 

 recovery is rare. 



Treatment that prevents late growth (199, 200), or 

 mulching the ground about trees tends to avert root- 

 killing. 



196. Killing of flower-buds. — Flower-buds are often 

 destroyed by cold while other parts of the plant are un- 

 injured. This frequently occurs in the peach, cherry, apri- 

 cot, nectarine and certain species of the plum in climates 

 of rather severe winters, especially after the buds have 



