. Manual of tree diseases . Trees. 142 MANUAL OF TREE DISEASES ing midsummer the cankers enlarge at the rate of about one- half inch in diameter each week. The usual shape of the canker is ellipsoidal (Fig. 17). The margin of the canker is usually regular and some- what raised. On smooth bark, the thin cork-layer is wrinkled, forming concen- tric rings about the central point of the canker. As the canker becomes larger, the bark splits and after a time falls away in shreds, leaving the wood bare. ^Vhen the fungus is working in the living tissues under the rough bark, there are no outward indic
. Manual of tree diseases . Trees. 142 MANUAL OF TREE DISEASES ing midsummer the cankers enlarge at the rate of about one- half inch in diameter each week. The usual shape of the canker is ellipsoidal (Fig. 17). The margin of the canker is usually regular and some- what raised. On smooth bark, the thin cork-layer is wrinkled, forming concen- tric rings about the central point of the canker. As the canker becomes larger, the bark splits and after a time falls away in shreds, leaving the wood bare. ^Vhen the fungus is working in the living tissues under the rough bark, there are no outward indications of its pres- ence until the fruiting-structuresare pro- duced in crevices of the bark. If the bark is peeled from the edge of a canker, the tawny mycelial fans are readily seen (Fig. 18). The invaded tissues are changed to a light brown in contrast to the normal light colored healthy tissue of the bark. The thick bark is reduced to a mass of shreds which are a uniform dark brown. The first layers of wood under the cankered areas also become brown. The effects of the disease on the general appearance of the tree are most noticeable during the summer when the trees are in leaf. In localities in which the disease is common, large numbers of the newly affected branches and twigs are girdled by the cankers during the late siunmer and the brown shriveled leaves hang to the limbs. This most striking. Fig. 17.—Endothia canker of 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 Rankin, W. Howard (William Howard), b. 1888. New York : The Macmillan Company
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