These are formed from a zone containing larger vessel elements produced by the cambium in the spring (lighter layer), followed by a zone containing smaller vessel elements (darker layer) produced during the late summer.

• 春季，形成层活动旺盛，形成的次生木质部细胞，管径大而壁厚，色泽较淡；夏末，形成层活动逐渐减弱，形成的次生木质部细胞，管径小而壁薄，色泽较深。