Developmental and Anatomical Studies on the Root of Platycodon grandiflorum A.DC

The development and the structures of the annual and the perennial tap roots of Platycodon grandiflorum were studied with the paraffin section and the semi-thin section.The results showed that the development of P.grandiflorumroot could be divided into four stages:promeristem,primary meristem,primary growth and secondary growth.The promeristem consists of three groups of initial cells;the primary meristem is composed of calyptrogens,primordial epidermis,periblem and plerome.The primary structure includes epidermis,cortex and stele.Parenchyma cells in cortex are dominant.The primary xylem is diarch. The secondary growth depends on activities of the vascular cambium and the cork cambium.The secondary structure includes periderm and secondary vascular tissue from the outside to the inside.Parenchyma cells are prominent in the secondary vascular tissue,and only small amount of vascular elements are scattered in them.The perennial roots have the similar structure to the annual one,but there are some differences in the length and the diameter of the tap root,the thickness of periderm and the area ratio between the xylem and the phloem.