The nature of the vascular cambium is discussed and the length of the elements in the secondary xylem related to the division and elongation cycles of the cambial fusiform initials. Particular attention is given to the activities of the storeyed cambium. The ontogeny of the storeyed cambium is described for Hoheria angustifolia Raoul. (Malvaceae). The transition from procambium to cambium was found to take place gradually, the meristem acquiring cambial characteristics over a number of internodes, some before and some after internodal elongation had ceased. The cambium is non storeyed at the commencement of secondary growth but later develops a storeyed pattern. Developmental changes in the cambium with radial growth were studied in Aeschynomene hispida Willd. (Papilionaceae). Repeated radial longitudinal divisions in the fusiform cambial initials in this plant produce a highly developed storeyed pattern with radial growth. The frequency of these divisions decreases with increasing distance from the stem centre. The mean length of the fusiform initials decreases slightly with radial growth. Variation in the size of the fusiform initials and vessel members was also investigated in Hoberia angustifolia. Mean length of the fusiform initials was found to remain constant with increasing distance from the stem centre but a slight decrease was observed with increasing height in the tree. Mean fusiform initial width showed an increase followed by a decrease with increasing height in the tree. The significance of these results is related to the division pattern in the storeyed cambium.