ABSTRACT
INTRODUCTION The germinating seedling originates from a bipolar embryo in which the radicle is situated at one pole and the plumule at the other (46, 213). The plumule is flanked by one or more cotyledons (32, 46). The meristematic cells of the root and shoot tips (47, 213-217) are the source of the cells which differentiate within the apical and sub-apical regions (215-220) into the primary tissues of the stem and root. The leaves and buds originate from surface layers at the margins of the shoot apex (215, 216, 218, 221) but lateral roots develop deep within the root, some distance from the root tip (222). The rates of cell division, differentiation, and maturation vary greatly within different regions of the root and shoot apices. Meristematic activity usually extends for some distance behind the apex.
