ClipArt ETC
"Stages in the development of the elements of the xylem. A, progressive steps in the development of a tracheal tube. 1, row of procambial or cambial cells that are to take part in the formation of a tube; 2, the same at a later stage enlarged in all dimensions; 3, the cells in 2 have grown larger, their cross-walls have been dissolved out, and the wall has become thickened and pitted; 4, the walls in 3 have become more thickened, the pits have an overhanging border, the walls have become lignified as indicated by the stippling, and finally the protoplasts have disappeared, and the tube is mature and dead." -Stevens, 1916

Xylem Development 1

"Stages in the development of the elements of the xylem. A, progressive steps in the development of…