Developmental Changes in the Fusiform Cambial Cells of some Tropical Trees

Abstract

Divisional activity, intrusive growth and loss of fusiform cambial cells have been studied in three tropical trees: Tectona grandis L.f. (Verbenaceae) , Gmelina arborea R oxb . (Verbenaceae) and Mangifera indica L. (Anacardiaceae) . Periclinal divisions of fusiform initials lead to the development of secondary xylem and phloem elements while anticlinal divisions enhance the number of cells to increase the circumference of cambial cylinder. In Tectona and Gmelina periclinal divisions occur seasonally, whereas in Mangifera the divisions are continuous. Anticlinal divisions are oblique and lateral with a great variation in the length of partition wall. Radial anticlinal divisions do occur sporadically in the fusiform initials of Tectona and Gmelina . The radial walls are relatively thick during dormant period. The cells elongate by intrusive growth at the vertical ends. Forking of cell tips and intrusion into the adjacent cells are commonly observed. Splitting of rays occurs by the intrusion of elongating cell tip into ray initials. Fusiform cambial cells undergo various structural changes during the periodic growth adjustments in the cambium. The rate of fusiform cambial cell loss is apparently high when the cambium is active.