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Meaning of black arm

black' arm"

Pronunciation: [key]
— Plant Pathol. Plant Pathol.
  1. a type or phase of bacterial blight of cotton, characterized by black, elongated lesions on the stem and branches, caused by a bacterium, Xanthomonas malvacearum.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.