地下茎加粗过程中形成三生结构，其异常结构是由于次生韧皮部外侧发生的额外形成层所致，其起源于薄壁细胞；
The growth of hypogeal stem contain tri-growth, and the anomalous secondary growth is the result of supernumerary cambium that derived from the outmost elements of secondary phloem.
初生木质部与初生韧皮部之间可见到2—3层排列规则或不规则的薄壁组织细胞，但是没有维管形成层的发生。
Between primary xylem and primary phloem there are 2-3 layers of parenchymatous cells, regularly or irregularly arranged, but no cambial zone can be recognized.
根的次生韧皮部则由筛胞和韧皮薄壁细胞组成。
The secondary phloem consisted of sieve cells and phloem parenchymas.
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