Polarised light micrograph of a cross section through the stem of the common reed (Phragmites australis). Phragmites is a perennial grass which is important for wildlife and is sometimes used for thatching. The central area of the stem is formed from aerenchyma which is a mesh-like structure which allows gaseous exchange within the plant and also provides buoyancy. Vascular bundles are arranged around the perimeter of the stem. Magnification: x28 at 10cm wide.