Identification of shoot apical meristem cells committed to form vascular elements in Pisum sativum L. and Vicia faba L.

A cytochemical study of naphthol AS-D esterases in vegetative shoot apices of Pisum sativum and Vicia faba L. has shown the presence of carboxyl esterases (E.C. 3.1.1.1.) in those meristem cells already committed to form vascular elements. These cells form a sequence linking the morphologically identifiable procambium to the cells of the tunica layers at a site either already identifiable as the next primordium or which will form the next primordium. The implications of this result are briefly discussed in relation to the control of primordia formation and procambial cell development.