A Sequential Study of Cell Divisions and Expansion Patterns on a Single Developing Shoot Apex of Vinca major

During the growth of a single developing vegetative apex of Vinca major, both the orientation and frequency of cell divisions, and the pattern of cell expansion, were observed using a non-destructive replica technique. Micrographs taken at daily intervals illustrate that the central region of the apical dome remains relatively inactive, except for a phase of cell division which occurs after 2 d of growth. The majority of growth takes place at the proximal regions of the dome from which develop the successive pairs of leaves. The developing leaf primordia are initiated by a series of divisions which occur at the periphery of the central dome and are oriented parallel to the axis of the subsequent leaves. The cells which develop into the outer leaf surface of the new leaves undergo expansion and these cells divide allowing for the formation of the new leaf. This paper describes the first high-resolution sequential study of cell patterns in a single developing plant apex.