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。
When the mosses are insufficient, tissue culture of mosses is a supplementary work worthy of consideration for expanding the resources of mosses. 用组织培养的方法增加藓类的数量是扩大藓类资源的一种有效补充办法。
