274 FUNDAMENTALS OF FRUIT PRODUCTION 



utilizing protection, natural or created, from winds, particularly those 

 prevailing in early winter, and the grower whose orchard is on an exposed 

 site should pay careful attention to the attainment of as complete 

 maturity as possible in his trees. Banking, though laborious and 

 expensive, is justified under threatening conditions. For trees already 

 damaged the best treatment is to cut away the injured bark and to cover 

 the exposed surfaces with grafting wax or paint and possibly to 

 bridge-graft. 



WINTER INJURY ASSOCIATED WITH DROUGHT 



In spite of the great water-retaining capacity of the tissues of the 

 most hardy deciduous fruits in a dormant state, they are not able to 

 withstand an indefinite amount of desiccation. Especially when the 

 evaporating power of the air is high they gradually lose water. This will 

 result eventually in a desiccation that may mean the death of the tissue 

 unless the water lost is replaced promptly. Recovery from winter 

 desiccation, or the ability to withstand long continued hard freezing 

 (physiological drought) or long continued winter drought (atmospheric), 

 depends therefore on a supply of available moisture upon which the 

 roots may draw. In many sections there is seldom, if ever, a winter 

 when soil moisture would be a limiting factor in this connection. In 

 others it is frequently a limiting factor and gives rise to those injuries that 

 are classed here as associated with winter drought. 



Fundamentally all injury to dormant tissues from cold is to be regarded as 

 induced by drying out. Paradoxically, it is generally the tissue containing the 

 most moisture that is most subject to damage. The injury, however, comes from 

 immaturity and not from excess moisture. Apparently there is a certain quan- 

 tum of water, varying with the kind of plant and with conditions, that is essential 

 to protoplasmic life and this is retained more tenaciously by mature tissue. 

 Hence, in considering winter injury a distinction must be drawn between mois- 

 ture in the plant tissues (water of composition and surplus moisture) and 

 moisture in the environment. Though the two are closely related, freezing 

 (drying out) of immature tissue in a moist environment should be distinguished 

 from freezing (drying out) due to dry environment though the final lethal 

 process is the same. 



Immaturity and Winter Drought 



Injury from drying out may have certain manifestations in agreement 

 with that from immaturity. It is, however, somewhat more evident 

 in the tops though it may extend to the trunk. Fruit buds in the apple 

 are killed more generally by this type of freezing than through imma- 

 turity. Wood formed the previous year suffers heavily; with more 

 extreme conditions the damage extends downward. Injury associated 

 with immaturity may start either on the young twigs or on the trunk. 



