Polarised light micrograph of a transverse section through a Parthenocissus sp. stem. Cutting the stem has released calcium oxalate crystals (rods), or raphides from the cells. 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: x110 when printed at 10 centimetres wide.