Polarised light micrograph of a transverse section of the stem of a Parthenocissus sp. plant showing calcium oxalate crystals (rods), or raphides, in the cell cytoplasm. Calcium oxalate crystals are common in the stems and leaves of many plants; they have no known metabolic function other than to serve as a means of disposal of excess calcium in the plant. Magnification: x1,110 when printed at 10 centimetres wide.