Mapping all procambial strands in serial transections of the six contiguous nodes below the tassel primordia of a young stem of Zea reveals the pattern that forms the vascular system. The disk of insertion and its subtended leaf primordium comprise the node. By means of a peripheral primary thickening meristem, each disk of insertion generates within itself concentric, successive waves of isolated procambial strands. These initially discrete procambia become linked into sympodial leaf traces by merging with procambia of the subtended leaf primordium and with procambia of adjacent waves of their own and of adjacent disks of insertion. Suspension of the procambial mergers with the scale leaf (the vegetative leaf adjacent to the tassel primordia) facilitates the process of recognizing the pattern to the succeeding waves of procambial initiation. The observation that the median, major lateral, bud, and intermediate traces of vegetative leaves appear to penetrate the disks of insertion to respectively decreasing depths has its basis in the fact that these sympodial leaf traces include respectively fewer successive procambial waves. Some of the procambia in the successive waves persist with blind ends. From them begins the dedifferentiation of the ground parenchyma into the horizontal procambial strands of the nodal plexus.