MARKET DISEASES OF FRUITS AND VEGETABLES 33 



threadlike fibers extending throughout the flesh. The whole net- 

 work, including the large bundles, constitutes the vascular (food- 

 and water-conducting) system of the fruit and, so long as the 

 fruit remains on the tree, is in direct connection with a similar 

 system in the twigs and branches. 



When freezing occurs the cells of the vascular system are 

 usually the first to be affected, especially if freezing takes place 

 rapidly ; and they may be the only ones affected. In cross section 

 this injury is shown by a brown discoloration of the 10 large 

 main bundles (pi. 10, Z>), the color being visible evidence that the 

 cells have been frozen to death. Similar browning may occur in 

 the smaller strands through the flesh and in the core tissues ; it is 

 frequently restricted to one side of the apple because of lower 

 temperature on that side. In more extreme cases all the tissues 

 may be affected; the flesh then shows throughout a solid color 

 which varies from bright golden brown to darker brown or almost 

 black, depending on the variety of apple and the severity and 

 freshness of the freezing injury (pi. 10, E) . The browned areas, in 

 whatever tissue found, usually have a water-soaked appearance 

 and if the injury is mild are translucent. 



EFFECT OF FREEZING AND THAWING 



It is generally believed that frozen apples are injured less by 

 gradual than by rapid thawing. While evidence on this question 

 is not altogether clear, somewhat more severe injury has been 

 found when the fruit is thawed at 65° F. than when it is thawed 

 at 32°. 



Apples that have been frozen are often dry and mealy, probably 

 because of loss of water through evaporation from the injured 

 tissues. The degree of mealiness increases with the amount of 

 freezing, but mealiness is not entirely absent even when freezing 

 is only slight. The flesh sometimes appears flaky or corky and 

 always lacks the normal crispness; in severely frozen specimens 

 it collapses and becomes viscid, soft, and mushy. 



If apples are frozen but not frozen to death, they may thaw 

 out with no apparent aftereffect except a slight softening of the 

 flesh. This softening, however, means that the prospective 

 storage life has been shortened. The amount of the reduction 

 depends on the variety, the degree of maturity of the fruit when 

 frozen, and the severity of the freezing. Unquestionably, apples 

 that have been solidly frozen throughout, even though for only a 

 short time, will not hold up so well in storage or for so long a 

 time as similar apples from the same orchard or the same storage 

 lot or shipment that have not been frozen. 



Apples should not be handled while frozen, because of the 

 danger of serious damage from bruising. Bruises produced in 

 this way frequently extend deep into the fruit, and the affected 

 flesh usually becomes brown, soft, and somewhat watery. 



FREEZING INJURY AND INTERNAL BREAK-DOWN 



' During January or even earlier and through the remainder of 

 the storage season, it may sometimes be difficult to distinguish 

 freezing injury from the condition known as internal break-down 

 due to overripeness. The difficulty will be greatest when there is 



