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Phases of wood formation in Qilian juniper in 2011. (A) Cambial zone (CZ) on 29 April; no new xylem cell production observed; (B) enlarging (EM) and wall-thickening (WT) cells on 10 July; (C) enlarging (EM) and wall-thickening (WT) cells on 10 July, under polarized light; (D) the current xylem tree ring consists entirely of mature cells (MC) on 2 October.
