OCCURRENCE OF SIEVE ELEMENTS IN PHLOEM RAYS

Solitary sieve elements or groups of sieve elements were encountered i n the rays of secondary phloem of Erythrina indica, Guazuma tomentosa, Acacia nilotica, Azadirachta indica, and Tectona grandis trees. These elements were short and possessed simple and compound sieve plates on their transverse to slightly oblique end walls. Each sieve tube eleme nt was associated with a single companion cell at their corners. Like axial sieve tube elements, the sieve tube elements of the rays showed slime (P-protein) plugs and cytoplasmic strands when functional and ma ssive deposition of callose on sieve plates in nonfunctional sieve tub e elements. The distribution pattern of these ray sieve elements diffe red among the species studied. The detailed structure and possible sig nificance of these elements are discussed.