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.
The secondary xylem of root is well developed, and there is supernumerary cambium around the vessels.
块根的次生木质部发达，导管周围存在额外形成层。
3
Secondary structure occurs in the root hair zone, and vascular cambium is formed from the parenchyma cells between the primary xylem and primary phloem;