300 FUNDAMENTALS OF FRUIT PRODUCTION 



clefts, that is to say, the sudden warming of the outer layers of the trunk 

 while the inside is still cold, is said to produce a different kind of injury, 

 known to foresters as a ''cup-shake." Here the cleavage instead of 

 being in a radial direction is along an annual ring, involving a smaller or 

 greater amount of the circumference. This form may possibly occur in 

 fruit trees but in most cases of separation along annual rings in such 

 plants the injury may be traced to direct killing just inside the cambium, 

 discussed under Black Heart. Even under natural conditions the cup- 

 shake is far less common than the frost crack. 



In connection with trunk splitting, the splitting of the bark while the 

 wood remains intact should be mentioned. As already indicated this is 

 generally in immature tissues, produced possibly at times by the same 

 conditions that induce trunk splitting but more frequently by the con- 

 ditions commonly associated with crown rot and crotch injury. It 

 should be understood, also, that splitting of the wood sometimes seems 

 to be associated to some extent with immaturity^^ and it may possibly, 

 as for example, when it occurs during protracted and intense cold, be due 

 to drying out. 



Summary. — Winter injury takes many different aspects, 10 more or 

 less distinct forms being considered in this discussion. Many different 

 environmental conditions are associated with winter injury, though for 

 convenience these may be .grouped in three classes : (1) conditions encour- 

 aging immaturity of tissues, (2) conditions leading to winter drought, 

 (3) conditions leading to premature quickening in late winter and early 

 spring. Certain sections or regions are particularly subject to extremes 

 of one kind or another. 



Injuries associated withimmaturity are especially common in the more 

 humid sections with short growing seasons. Plants adapted to com- 

 paratively long growing seasons when taken to sections with shorter 

 growing seasons are particularly subject to injuries of this character. 

 "Second growth" is hkely to be immature and subject to winter injury. 

 Cultural practices which encourage late vegetative growth should be 

 avoided in regions where immaturity is a frequent problem. Crown 

 injury and crotch injury are in most cases associated with immaturity of 

 tissues at the affected points. Wind and variation in temperature 

 between different sides of the limb or trunk may be contributing factors. 

 Treatment for these localized injuries should be both preventive and 

 remedial. 



Injuries due to winter drought are especially common in sections 

 like the Dakotas and Wyoming where winter precipitation is low, the 

 snow covering scanty and the evaporating power of the air high. The 

 tissues are desiccated by the cold dry winds and recovery of turgidity 

 is difficult or impossible because of low soil moisture, deep soil freezing 

 and the inability of the conducting system to function while frozen. 



