Early ontogeny of vascular cambium II.Aucuba japonica andWeigela coraeensis

InAucuba andWeigela the six vascular bundles distributed as a hexagon become connected tangentially by meristematic cells into a procambial cylinder in the early stage. In the tangential view, the procambial cylinder shows a rather homogeneous structure. InAucuba, some cells of the procambium elongate in a relatively earlier stage and the rest also elongate during subsequent stages. All of these cells have tapering end walls. Then some long cells divide transversely and form two systems in the vascular meristem, one made up of long cells and the other of short ones. The long cells become the fusiform initials and the short cells, the ray initials. InWeigela, the homogeneous procambium is organized in the later stages into two systems, one of long cells and the other of short cells in axial files. Most of the long cells have tapering end walls and the short cells transverse end walls. Some of the short cells elongate to intrude between adjacent cells and become long cells. The long cells become the fusiform initials. Radial divisions in some short cells occur occasionally. Some of these cells elongate and the rest remain in the axial files. Some short cells in the axial files are vertically separated from each other by the elongation of adjacent long cells. however, this occurs infrequently and the height of axial files is still several decades of cells. Short cells in axial files eventually become ray initials.