Diseases of deciduous forest trees Diseases of deciduous forest trees diseasesofdecidu00schruoft Year: 1909 DISEASES CAUSED BY WOUND FUNGI. 41 SOFT ROT OF OAKS CAUSED BY POLYPORUS OBTUSUS. A number of species of the black oaks, notably Quercus marilandica Muench. and Q. velutina Lam., are affected with a disease of the heart- wood which has been determined by Spaulding (94) to be due to Poly- j)orus ohtusus Berk. Diseased trees have been found in the eastern part of the United States, and notably in the central Mississippi Val- ley; a large number of trees are usually found aft'ected in a lo
Diseases of deciduous forest trees Diseases of deciduous forest trees diseasesofdecidu00schruoft Year: 1909 DISEASES CAUSED BY WOUND FUNGI. 41 SOFT ROT OF OAKS CAUSED BY POLYPORUS OBTUSUS. A number of species of the black oaks, notably Quercus marilandica Muench. and Q. velutina Lam., are affected with a disease of the heart- wood which has been determined by Spaulding (94) to be due to Poly- j)orus ohtusus Berk. Diseased trees have been found in the eastern part of the United States, and notably in the central Mississippi Val- ley; a large number of trees are usually found aft'ected in a locality. The spores of the fungus germinate in the burrows of an oak-boring insect {Prionoxystus rohiniae Peck.). The fungus grows in the borings and follows the in- sect burrow until it reaches the heartwood of the tree; it then spreads out from this point, both up and down the trunk, and gradually brings about a form of soft rot. (Fig. 5.) The dis- eased wood is lighter in color than the heartwood of the healthy tree, and in its last stages turns almost white. 'The diseased wood retains itshbrous appearance, but breaks much eas- ier than does the healthy wood. It does not have the SnrinKage cracks Fig. 5.—a living blacu oak tree with a sporophore of Po/j/porits which are so charac- obtusus growing out of the opening of an insect burrow. teristic of some of the wood rots; neither does the affected tissue crumble between the fingers nor break very easily into small flakes ' (94). The fimgus grows in the trees rapidly, extending up and down in the heartwood and growing outward until it reaches the sapwood. Affected trees are weakened to such an extent within one or two years after their first attack that the slightest windstorm causes the trunks to break. The sporophore of Polyporus obtusus is a very characteristic one. It usually appears at the original insect burrow, where it forms a thick, more or less hoof shaped shelf; in some cases two or three shelves may form, one immed
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