CAMBIAL ANATOMY AND ABSENCE OF RAYS IN THE STEM OF BOERHAAVIA SPECIES(NYCTAGINACEAE)

Structure of vascular cambium and its derivatives in Boerhaavia diffus a L., B. verticillata Poir. and B. rependa Willd. (Nyctaginaceae) was studied by anatomical methods. The stem revealed anomalous secondary g rowth characterised by the development of successive rings of xylem an d phloem. The cambium was exclusively composed of fusiform initials gi ving rise to rayless secondary vascular tissues. While undergoing peri clinal divisions cambium appeared nonstoried but remained storied when the divisions ceased. Each successive ring of cambium was originated from the outermost phloem parenchyma cells. The cambial ring was funct ionally segmented into fascicular and interfascicular regions, the for mer mainly producing conducting elements of xylem and phloem and the l atter giving rise to parenchyma cells. The parenchyma cells on the xyl em side developed into conjunctive tissue following thickening and lig nification of cell walls. However, in B. verticillata and B. rependa t he parenchyma cells on the pholem side also became lignified. In B. di ffusa parenchyma cells did not undergo lignification. As a result, alt ernate bands of lignified and parenchyma bands became distinct in the stem. Vessel elements were short with simple perforation plate on slig htly oblique to transverse endwall. Sieve tube members were slightly s horter as compared to the fusiform cambial cells.