Aspect of a xylem bundle observed with the objective of 40x. The cell walls of the vascular elements that form the bundle are clearly visible due to the red-stained reinforcements of lignin. More externally are placed the elements of the metaxylem, showing complicated reinforcements in the cell wall (it can be easier observed in the microphotography observed with the objective of 10x). More internally are located the elements of the protoxylem, provided with reinforcements in form of ring or spiral. Between these elements are placed cells of the xylematic parenchyma (yellow)