. Manual of fruit diseases . Fruit. APPLE DISEASES 131 critical notice be taken, however, it will be seen that the pustules on the superficial bark-canker are of an open, saucer-shaped tj'pe, while on the black-rot canker they are closed, flask-shaped bodies. The dead bark clings tightly to the limb for some time. Later, bits of bark fall from the tree. Old cankers usually show considerable checking of the bark (Fig. 34); these crevices are short and sometimes extend at right angles to the long axis of the affected limb. Cause. The fungus Myxosporium corticolum is responsible for the superfici
. Manual of fruit diseases . Fruit. APPLE DISEASES 131 critical notice be taken, however, it will be seen that the pustules on the superficial bark-canker are of an open, saucer-shaped tj'pe, while on the black-rot canker they are closed, flask-shaped bodies. The dead bark clings tightly to the limb for some time. Later, bits of bark fall from the tree. Old cankers usually show considerable checking of the bark (Fig. 34); these crevices are short and sometimes extend at right angles to the long axis of the affected limb. Cause. The fungus Myxosporium corticolum is responsible for the superficial bark-canker of the apple and the pear. The known facts connected with its life-history and habits are few. The mycelium of the fungus grows in the outermost bark- tissues only, never reaching the cambium. Scarcely before it penetrates to an ap- preciable depth its progress is halted by a cork-layer developed by the tree in response to the stimulation induced by the invader. This plate of cork is ap- parently never penetrated by the fungus, therefore its attacks are confined to the surface cells. The affected tissue is killed and eventually it sloughs away. In this process the cork-layer marks the line of cleavage. During its course of develop- ment the fungus forms fruiting bodies, acervuli, just beneath the surface of the bark. At maturity these break through the bark and expose a saucer-shaped interior. Conidia arise from the inner wall of this cavity; and in the moist weather of spring the spores ooze forth in white masses. These spores. Fig. 34. — Superficial 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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