. Manual of fruit diseases . Fruit. 38 MANUAL OF FRUIT DISEASES death of the bark on the southwest or sun-exposed side of a tree. The frosted bark may peel, exposing the discolored sap- wood ; or sometimes it adheres closely to the wood and a sunken, cankered area is thus formed. In some cases the sapwood is killed and the cambium is left alive to form new wood outside the dead area. The sapwood is stained by the diffusion into it of some substance apparently originating in the protoplasm of the affected tissues. When the wood is thus discolored it is called black-heart. This type of injury is
. Manual of fruit diseases . Fruit. 38 MANUAL OF FRUIT DISEASES death of the bark on the southwest or sun-exposed side of a tree. The frosted bark may peel, exposing the discolored sap- wood ; or sometimes it adheres closely to the wood and a sunken, cankered area is thus formed. In some cases the sapwood is killed and the cambium is left alive to form new wood outside the dead area. The sapwood is stained by the diffusion into it of some substance apparently originating in the protoplasm of the affected tissues. When the wood is thus discolored it is called black-heart. This type of injury is common in the northern United States. Frost- killed areas in the bark are commonly inhabited by sapro- phji:ic and weakly parasitic organisms, prominent among which is the New York apple- tree canker fungus, Physalospora Cydonice. The name sun-scald owes its origin to the common belief that it is due to some interaction of sun and cold on the sunny side of the tree in late winter. It in- volves the crotches and the ad- joining sun-exposed bark of the trunk and limbs as well. The Ben Davis, Stark and Twenty Ounce varieties are generally regarded as most susceptible to sun-scald. Trees leaning to the northeast are most severely injured. Twigs are killed by winter temperatures. The last season's growth is killed back to a definite point. This occurs every year to some extent. It depends largely on whether or not the wood ripens properly in the Fig. 9. — Apple-tree showing frost- cankers at Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hesler, L. R. (Lexemuel Ray); Whetzel, Herbert Hice, 1877-1944. New York : Macmillan
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