Abstract: Developmental studies nave been made of anomalous secondary thickening in the root of medicinal species of Fhytclacca acincsa Rcxb. in order to bring about the initiation and formation of the anomalous secondary vascular cylinder. It has been found that both the primary and the early secondary structures resemble those of most of the dicotyledons. Subsequently, 5-7 rings of anomalous cambia, however, develop in the outside of the vascular cylinder centrifugally. The first ring initials from the parenchyma and ray cells of the secondary phloem, and the succeeding ones arise periodically by periclinal divisions in a layer of parenchyma cells two or three cells beyond the outmost intact phloem derived from the current cambium. Each cambium forms a few of parenchyma cells on both sides before it forms derivatives into lignified xylem elements or conductive elements of the phloem. The parenchyma thus formed toward the outside later becomes the site of the origin of the succeeding cambium. The cambium produces fasicular strands, showing centrifugal differentiation of xylem and centripetal differentiation of phloem on opposite sides of the cambial layer, and parenchyma conjuctive cells between the fascicular areas. In both xylem and phloem the younger elemerts are closer to the cambium than the older ones. All the parenchyma conjuctive cells and parenchyma cells in the fascicular strands are rich in starch grains.