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[C19: from mes(o)- + Greek arkhē beginning]
mes•arch(ˈmɛz ɑrk, ˈmɛs-, ˈmi zɑrk, -sɑrk)
1. (of a primary xylem or root) developing from both the periphery and the center; having older cells surrounded by younger cells.
2. (of a life form) originating in a habitat with a moderate moisture supply.