Studies were conducted on developmental anatomy in order to elucidate the differentiation pattern of vascular cambial initials in the first internode of Acer saccharinum. The procambium is transformed from an early homogeneous structure composed of short cells into a heterogeneous structure later having long and short cells. In the transformation process, some cells are elongating while the other cells form axial strands by repeated transverse divisions. The long cells with tapering ends differentiate into cambial fusiform initials and the short cells in axial strands into ray initials. The differentiation pattern of vascular cambium in the first internode of Acer sac charinum does not resemble that of Acer pseudoplatanus in the same genus because the ray initials originate from the segmentation of long cells in the later species.