Development Anatomy of Achyranthes bidentata Roots

The developmental process of Achyranthes bidentata roots was examined by anatomical methods.It was shown that the development of A.bidentata roots included five developmental stages,promeristem,primary meristem,primary structure,secondary structure and tertiary growth stages.The promeristem possessed the characters of typical cambium cells,the primeristem included calyptrogens,dermatogen and plerome,and the primary structure was composed of epidermis,cortex and stele.The endodermis had clear Casparian strips on its cells.In most cases,the primary xylem was diarch and the secondary structure included periderm and secondary vascular tissue from the outer to the inner and its cork cambium developed from pericycle cells recovering their dividing capacity and vascular tissue dominated in the primary structure;A.bidentata roots further thickened because of the occurrence and differentiation of their tertiary structure.The first ring of extra cambium developed from parenchymatous and ray cells outside the secondary phloem and each following ring of extra cambium developed from parenchymatous cells deriving from its previous ring of extra cambium.The rings of extra cambium presented no differentiation into spindle-shaped and ray archaeocytes and appeared longitudinally overlapped.The tertiary vascular bundles were regularly,concentrically and centrifugally arranged and partitioned with connective parenchyma whose ring numbers were the same as that of extra cambium.