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Barrier zones of axial parenchyma, were common in sapwood of trees which had recovered from vascular infections. They were a consistent feature in a representative sample of vascular wilt diseases when trees expressed some resistance. Vascular wilt diseases caused by Ceratocystis ulmi, C. coerulescens, Vertici/lium albo-{ltrum, and Fusarium oxysporum were studied.
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Tippett et al. (1981) studied this question.
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