Water parsnip rhizome. Light micrograph of a cross-section through an underwater rhizome of the lesser water parsnip (Berula erecta). The rhizome has a matrix of plates of cells (blue), which enclose vascular bundles with supporting fibres. The plates enclose air spaces (lacunae) which store oxygen. This portion of the rhizome shows two diaphragms which consist of a layer of dead cells (dark blue) that give support to the rhizome. Magnification: x100 when printed at 10 centimetres across.