ONTOGENY OF THE VASCULAR BUNDLES AND CONTIGUOUS TISSUES IN THE MAIZE LEAF BLADE

The patterns of initiation and early development of the minor and majo r veins in the hat portion of the leaf blade of maize (Zea mays L.) fo llow similar patterns. The veins and their associated bundle sheath ce lls commonly arise from cell assemblages derived from a single cell li neage, or longitudinal file of cells, rather than from two ''half vein units'' derived from different cell lineages. In addition, apparently , none of the vascular cells derived from the procambium is directly r elated ontogenetically to a bundle sheath cell. In veins derived from larger cell assemblages, the lateral bundle sheath cells are more clos ely related ontogenetically to the mesophyll cells, which are derived from the ground meristem, than to the vascular cells, which are derive d from procambium. The bundle sheath cells, accordingly, are interpret ed as being ground meristem in origin.