Cambial variant in the stem of Antigonon leptopus H. & A. (Polygonaceae)

The stem of Antigonon leptopus H. & A. was composed of five to six successive cambial rings. Cambium was storied with axially elongated fusiform cambial cells and horizontally arranged ray cambial cells. Each cambial ring was functionally divided into fascicular and interfascicular regions; the former giving rise to xylem elements inside and phloem elements outside while the latter producing parenchyma cells on either side. New cambial rings were originated from cortical parenchyma after the cessation of cell divisions in the preceding ring. Prior to the initiation of new cambium, the interfascicular region of the previous cambium disappear while fascicular region maintained its radial arrangement. The nonfunctional phloem from the innermost cambial rings underwent obliteration. Xylem was composed of vessel elements, vascicentric tracheids, living fibres, axial and ray parenchyma cells. Vessels were dimorphic in nature with notably large and narrow vessel elements.