Levels of maturation of protoxylem and protophloem elements in aerial roots of Cissus and Ficus

Abstract

The levels of maturation of protophloem and protoxylem elements in the adventitious aerial roots of Cissus quadrangularis and Ficus benghalensis are reported on the basis of serial sections of a large number of root apices. The aerial roots of Cissus resemble the roots of other taxa that have been studied in having the mature protophloem elements at a level distal to that where maturation of protoxylem elements occurs; those of Ficus show an inverse order, protophloem elements occurring proximal to protoxylem elements. In both the species studied, wide variations in levels of maturation of protophloem elements are noted in some roots, while others show a wide variation in levels of protoxylem elements. It is suggested that rates of growth and rates of the maturation process operating independently are involved.