. Manual of tree diseases . Trees. ELM DISEASES 153 every season on the leaves in late autumn just before the leaves fall. The first indications of the spots are seen on the upper surface of the leaf. The dead leaf-tissue is grayish, and either scat- tered over the spot or grouped in the center are one or more black pustules (Fig. 21). The under sur- face of the leaf shows no evidence of the spot until later in the season, when brown dead areas appear with a few raised pustules. After the leaves fall to the ground, fruiting-bodies containing ascospores de- velop which are the source of primary
. Manual of tree diseases . Trees. ELM DISEASES 153 every season on the leaves in late autumn just before the leaves fall. The first indications of the spots are seen on the upper surface of the leaf. The dead leaf-tissue is grayish, and either scat- tered over the spot or grouped in the center are one or more black pustules (Fig. 21). The under sur- face of the leaf shows no evidence of the spot until later in the season, when brown dead areas appear with a few raised pustules. After the leaves fall to the ground, fruiting-bodies containing ascospores de- velop which are the source of primary infection the following spring. The pycnidia of many species of fungi are found on elm leaves and it is not known which one of these is con- nected with the Gnomonia. For a further discussion of leaf-spots and their con- trol, see page 27. Fig. 22. —Powdery mildew of elm. Powdery Mildews Caused by Uncinula macrospora Peck, Microsphoera alni (Wallr.) Salmon and Phyllactinia corylea (Pers.) Karst. Three species of the powdery mildew fungi attack the leaves of elms in the United States. In the case of all three species the characteristics, so far as visible to the unaided eye, are. 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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