Structural and developmental studies on cambial variant in Pupalia lappacea (Amaranthaceae)

Secondary growth in the stem of Pupalia lappacea (L.) Juss. (Amaranthaceae) resulted in the development of successive rings of cambium. The cambium wa s storied, consisting only of fusiform cambial cells. Cessation of cell div ision in each cambial ring was followed by development of a new cambium fro m the outermost phloem parenchyma produced by the preceding cambium. Absenc e of ray cambial cells resulted in development of rayless secondary xylem a nd phloem. Development of conducting elements of xylem and phloem was restr icted to the fascicular sector of cambial ring. Interfascicular sector of c ambium gave rise to xylem fibres centripetally and axial parenchyma centrif ugally. Xylem fibres retained their nucleus even after lignification of cel l walls. Raylessness of the stem and possible significance of nucleated fib res are discussed.