It is constantly replaced by newly formed cells as the older tissue is sloughed off with growth of the root through the soil. 随着根尖的生长，根冠外层的薄壁细胞与土壤颗粒磨擦，不断脱落，死亡，由其内的分生组织细胞不断分裂，补充到根冠，使根冠保持一定的厚度。
The vascular cambium extends to form a complete ring of meristematic tissue around the stem, the separate vascular bundles being linked by interfascicular cambium. 维管形成层向两侧延伸直至形成一个茎内的分生组织环，各个维管束被束间形成层联系在一起。
