myeloplast

[mīə-lə-plăst′]
n.
  1. Any of the various cells that occur in the bone marrow and that form white blood cells, especially those cells in an early stage of development.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.