答案:年轮:维管形成层的活动受气候因素的影响,而常有周期性的变化,在一个生长期中所产生的次生木质部(包括早材和晚材)就构成一个年轮,在横切面上,表现为不同颜色的同心圆环。annual ring:Concentric circles visible in cross-sections of woody stems or trunks. Each layer of early wood from the next growing season makes an abrupt contrast with the late wood before it, thus leading to the perception of rings.