A Complete Collection of 100000 Whys
Fav十万个为什么
为什么树干会有年轮？
树干年轮的形成主要与形成层的季节性活动、气候条件的变化以及细胞生长的差异有关。
1、形成层的季节性活动：树木的形成层在春夏季节分裂活跃，产生疏松、色浅的春材；秋冬季节分裂减缓，形成致密、色深的秋材，两者结合形成年轮。
2、气候条件的变化：温度、降水等气候因素直接影响形成层的活动。气候适宜时，年轮较宽；气候恶劣时，年轮较窄，反映了环境变化。
3、细胞生长的差异：不同季节形成层细胞的分裂速度和大小不同，导致木质部细胞的排列和密度差异，从而形成年轮的疏密变化。
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