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Cross-sections of Picea mariana at ×200: (A) developing xylem in mid-July, mature tracheids (Ma), wall thickening tracheids (Wt), radial enlargement tracheids (Re), cambial zone (Cz) and phloem (Ph); (B) cambial zone during dormancy at the beginning of May; (C) cambial zone during cell division at the end of May; (D) cambial zone at the end of cell division in mid-July. Scale bars = 30 µm.
