Cambial variants in the roots of Glinus lotoides L. and G. oppositifolius (L.) A. DC. (Molluginaceae)

Structure and development of successive cambia and their derivatives are studied histologically in the root of two species of Glinus (Molluginaceae). In both species first ring of cambium functions for a short time followed by the development of second ring from the cortical parenchyma. The subsequent cambial rings formed followed the similar pattern of development. The mature roots are composed of three to five successive rings of xylem alternating with phloem. Absence of ray initials in the cambium leads to the development of rayless xylem and phloem. Xylem consists of vessel elements, tracheids, libriform fibres, fibre tracheids and axial parenchyma. In transverse view vessels appear oval to circular and solitary in G. lotoides and angular, narrow and mostly in radial multiples in G. oppositifolius. Xylem fibres retain their nucleus even after the formation of secondary walls in both the species. Storage of starch in the lumen is a characteristic feature of fibres. The significance of successive cambia, rayless xylem and nucleated xylem fibres is discussed in relation to the plant habit.