Studies on the developmental anatomy of Dioscorea sansibarensis Pax (Dioscoreaceae)

Certain developmental and anatomical studies on D. sansibarensis Pax are briefly reported. (1) Stem diameter, internodal length, vessel diameter, distribution and number of vascular bundles in internodes (from base to apex) are determined. There is no correlation between vessel size and stem diameter. Cut stems left in water develop tyloses. (2) Roots are all polyarch. The development and structure of the vessels are discussed. Xylem and phloem differentiation in the root tip is determined. A central meristem at the root apex gives rise to the different tissues in the root. Raphide development in root cortex is traced. (3) Both alternate and opposite leaf arrangements occur, sometimes on the same plant, and there is a correlation between stem thickness and leaf arrangement. During leaf development the lamina length exceeds the width, but the two dimensions reach their maximum size at the same time. The acuminate leaf-tip matures before the rest of the leaf. Stomatal development is traced.