. Manual of tree diseases . Trees. 224 MANUAL OF TREE DISEASES maple are rarely if ever affected, even when growing among red and silver maples which are severely infected. This sub- stantiates the results of investigations in Europe which show that there are various strains of the tar-spot fimgus. These strains show preference for certain species of maples, but in other respects are indistinguishable from one another. Symptoms. The first evidence of the developing spots on the maple leaves are light green or yellowish areas. In the summer the spots become black on the upper surface of the lea
. Manual of tree diseases . Trees. 224 MANUAL OF TREE DISEASES maple are rarely if ever affected, even when growing among red and silver maples which are severely infected. This sub- stantiates the results of investigations in Europe which show that there are various strains of the tar-spot fimgus. These strains show preference for certain species of maples, but in other respects are indistinguishable from one another. Symptoms. The first evidence of the developing spots on the maple leaves are light green or yellowish areas. In the summer the spots become black on the upper surface of the leaf due to the black mycelium of the fungus. The surface of the tar-like spots is wrinkled with anastomos- ing furrows and somewhat raised above the surface of the leaf. The spots are usually a quarter or half inch across (Fig. 36). Cause. The tar leaf- spot of maples is caused by the fungus Rhytisma acerinum. Spores are borne free on the upper surface of the black mass of fungous tissue as it develops on the leaf. It is not known whether these spores infect other leaves or not. But from the number of leaves affected on some trees, it seems certain that these spores must account for the general prevalence of the infections. When the spotted leaves fall. Fig. 36. — Tar leaf-spot 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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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1918
