Developmental and Anatomical Studies on the Root of Polygala tenuifolia Willd.

The root developmental process and root structure of one-year,two-year and three-year Polygala tenuifolia Willd.were studied with paraffin sectioning.It was shown that the apical promeristem consisted of three groups of initials,and they possessed the typical cell characteristics of meristem.The primary meristem consisted of calyptrogen,primordial epidermis,periblem and plerome;while the primary structure consisted of epidermis,cortex and central cylinder,and primary xylem was diarch.The progress of the secondary growth depended on the activity of vascular cambium and cork cambium.The secondary structure included periderm and secondary vascular tissue from the outer to the inner.There were three characteristics of secondary structure of P.tenuifolia:the secondary phloem had major part of secondary vascular tissue,among which the secondary phloem contained mainly parenchyma with abundant storage,and the storage became more and more with the age adding,thus the parenchyma of three-year root had the most storage;the areas of periderm,secondary phloem and secondary xylem increased with the root-year increasing,whereas the area ratio of phloem and xylem had a trend from lower to higher,which was the obvious feature of P.tenuifolia;P.tenuifolia had developed periderm which with thick cork,and secondary xylem contained mainly vessels and fibers.The vessels distributed frequently and had wide diameter.The structure features of cork and secondary xylem adapted to the xeromorphic characteristics of P.tenuiflia.