Cambial Activity and Developmental Changes in Ray Initials of Some Tropical Trees

Abstract

Summary Structure, divisional activity and dimensional variations of ray initials in Tectona grandis L., Gmelina arborea Roxb. and Mangifera indica L. have been studied in relation to annual seasonal cycle of cambium. Resting ray initials have thick and beaded walls. Additive and multiplicative divisions in active ray initials lead to vascular ray differentiation and an increase in ray size respectively. New secondary rays originate primarily by division of ends and sides of fusiform initials. Multiseriate rays develop through the transverse and vertical divisions of ray initial precursor cells. Fusion between tangentially and radially adjacent rays occurs following the loss of intervening fusiform initials. The mean height and the average number of rays are significantly greater in active cambium. The seasonal variations in ray height is discussed in comparison with the length of fusiform initials.