. Diseases of economic plants. Plant diseases. 42 Diseases of Economic Plants The Lowell, Isham, Smith Cider, Yellow Transparent, Jonathan, and Willow Twig are especially susceptible varieties, while Celestia, Buckingham, Mammoth Black Twig, White Winter Pearmain, Winesap, and Ben Davis are resistant, the last almost en- tii-ely so. In general the crab vari- eties are more susceptible than others. ' ^ Black-rot, canker ^^^ ^^ {Physalo- spora cydonice Arn., Sphceropsis).— In many respects this disease closely resembles the bitter-rot, particu- larly in that it appears both as rot of the fruit a
. Diseases of economic plants. Plant diseases. 42 Diseases of Economic Plants The Lowell, Isham, Smith Cider, Yellow Transparent, Jonathan, and Willow Twig are especially susceptible varieties, while Celestia, Buckingham, Mammoth Black Twig, White Winter Pearmain, Winesap, and Ben Davis are resistant, the last almost en- tii-ely so. In general the crab vari- eties are more susceptible than others. ' ^ Black-rot, canker ^^^ ^^ {Physalo- spora cydonice Arn., Sphceropsis).— In many respects this disease closely resembles the bitter-rot, particu- larly in that it appears both as rot of the fruit and as cankers upon the limbs. In some instances it also appears as a twig blight and as a leaf spot. As seen under the hand lens the coils of exuding spores are black, instead of pink, as is the case with bitter-rot. A compound microscope is necessary to bring out other distinguishing characters. The limb cankers, first studied by Paddock, consist of sweUings, with the bark rough, and black. In other cases the black, decayed wood from which the bark has dis- appeared is exposed. This cankerous infection sometimes ex- tends for nearly a meter along the branch, and occasionally girdles it. When occurring upon the trunk or main branches it is called black-rot body-blight. The Tolman Sweet is said to be quite resistant to canker, while Twenty Ounce is very susceptible. Four other va- rieties range in susceptibility as follows: Baldwin, Wagener, Greening, King. Black-rot twig-blight somewhat resembles fire-blight with. Fig. 17. — Apple black-rot canker showing numer- ous pycnidia. After 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 Stevens, Frank Lincoln, 1871-1934; Hall, John Galentine, 1870-. New York, Macmillan
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