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Meaning of protoxylem

pro•to•xy•lem

Pronunciation: (prō"tu-zī'lum, -lem), [key]
— n. Bot.
  1. the part of the primary xylem that develops first, consisting of narrow, thin-walled cells.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.