. The bitter rot of apples. Apples; Bitter-rot. 32 THE BITTEE EOT OF APPLES. the humus compounds. It is probably one of the decomposition prod- ucts which forms when the bark and cambium are killed and which infiltrates the wood. One finds numerous fungous hyphae in the medullary ray cells and the larger vessels, but at this stage it is not possible to say whether these are hyphee of the bitter-rot fungus. Further studies in this direction are being made. The formation of the cankered spot probably starts at some small wound (or branch, as stated above). The fungus begins to grow in the living
. The bitter rot of apples. Apples; Bitter-rot. 32 THE BITTEE EOT OF APPLES. the humus compounds. It is probably one of the decomposition prod- ucts which forms when the bark and cambium are killed and which infiltrates the wood. One finds numerous fungous hyphae in the medullary ray cells and the larger vessels, but at this stage it is not possible to say whether these are hyphee of the bitter-rot fungus. Further studies in this direction are being made. The formation of the cankered spot probably starts at some small wound (or branch, as stated above). The fungus begins to grow in the living bark and kills the bark and the cambium. As a result no new wood is formed at the point where the cambium is killed (see PI. VIII. fig. 1). and a small depression forms as the wood at the edges of the dead cambium increases in thickness. As the fungus grows out from the original point of infection, more and more bark and cambium are killed, until at the end of the growing season a large spot on the limb is dead. Since there is always a small series of wood cells formed at the beginning of the year during which the attack takes place, the fungus probably starts to grow in the bark earhT in June. (See fig. 6.) The majority of the cankers found during the last summer probably were started two years ago. During the first year the fungus made very little headway. A very small central area was killed, generally around and in- cluding a small branch. The following year the larger part of the canker was formed. Whether the cankers will con- tinue to increase in size is as yet undetermined, but it does not seem probable, for if such were the case cankers three or more years old ought to have been secured in the orchards where the bitter rot has been common for manv Fig -Diagrammatic cross section of apple canker. RELATION OF THE CANKERS TO THE BITTER ROT. The discovery of the cankers was brought about directly by tracing groups of diseased apples to these sunken areas on apple
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