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Fine Structure of Ceratocystis ulmi in Elm Wood. Charles R. Krause, Research Assistant, Plant Science Research Division, ARS, USDA, Delaware, Ohio 43015; Charles L. Wilson, Research Plant Pathologist, Plant Science Research Division, ARS, USDA, Delaware, Ohio 43015. Phytopathology 62:1253-1256. Accepted for publication 10 May 1972. DOI: 10.1094/Phyto-62-1253.

Direct penetration of vessel cell walls and invasion of peritracheal parenchyma cells of Ulmus americana by Ceratocystis ulmi were observed 2 weeks after inoculation. An appressoriumlike structure was apparent when hyphae penetrated pit membranes. A dark-staining area was formed around hyphae in response to invasion of parenchymal cells. C. ulmi caused little over-all damage to cell walls.