Studies on the Developmental Anatomy of Rhizome of Dioscorea zingiberensis and Its Histochemistry

The tip of rhizome of Dioscorea zingiberensis C.H.Wright is surrounded by lepises.The cells derived from primordial meristem forms protoderm,ground meristem and dispersed procambium strands.The primary structure of the rhizome is includes epidermis,ground tissue and dispersed vascular bundles.There is primary thickening meristem at the lower part of rhizome tip under protoderm.The increase of cell number derived from primary thickening meristem and the enlargement of cells volume make the rhizome thicken rapidly.The mature rhizome is composed of periderm,ground tissue and vascular bundles.The periderm consists of phellem,phellogen and phelloderm;the ground tissue is of parenchyma;vascular bundle belongs to closed vascular bundle.Dioscin exists mainly in parenchyma cells of ground tissue.The primordial meristem and the procambium strand do not contain dioscin and the xylem and the phloem fiber of the vascular bundle do not contain dioscin either,but the life cells of phloem and the cells of vascular bundle sheath accumulate dioscin.Dioscin does not exist in the form of granule in ground meristem near the tip of rhizome,but granulous dioscin is formed in the cells of mature ground tissue.Dioscin that accumulated and distributed in ground tissue with small vascular bundle is the most abundant in the rhizome.The amount of dioscin of biennial is higher than that of annual rhizome.