36 MANUAL OF FRUIT DISEASES 
signs of injury from low temperatures. But these varieties are 
not invariably injured; and on the other hand those varieties 
omitted from the list are not always free from the trouble. 
Frost-injury seems to be confined largely to orchards between 
the ages of eight and thirty years. High-headed, severely 
pruned individuals of any variety on wind-exposed locations 
are most liable to the difficulty. Therefore, factors other than 
the nature of the variety condition the injury under con- 
sideration. 
The réle of frost-injury in fruit crop-production is a promi- 
nent and important one. Growers of fruits in practically all 
temperate and even in semi-tropical regions know and fear 
this trouble. But not every one appreciates the actual damage 
done in each case. It is only after hard disastrous winters such 
as were experienced in the East in 1903-1904, 1904-1905 and 
1906-1907 that general complaints and appeals for help are 
made. Trees are severely injured and often killed in the ex- 
tremes of winter temperatures of the northerly sections. In 
warmer regions late frosts sometimes entail heavy losses. 
Symptoms. 
Frost-injury involves all parts of the tree. Injury to aérial 
parts only are evident to the casual observer. A reliable symp- 
tom of fatal injury evident at the end of winter is not definitely 
known. Trees may appear entirely healthy, but on cutting 
into the bark above the snow line discoloration in the cambial 
region will be found. ‘Trees, especially in low spots, affected 
by frost fail to start in the spring or they may make only a- 
feeble growth. As the season advances they look unhealthy, 
the foliage is yellow, and finally death of the whole tree ensues 
(Fig. 8). Often a single branch or one side of a tree only is. 
afflicted. Such trees on closer examination show frost-injured 
areas or cankers at one or more places (Fig. 9). 
Injuries may occur chiefly on the southwest side of trees at - 
a point midway between the crown and head, or they may be 
