What is "aerenchyma"

Aerenchym \A"["e]r*en`chym\, ||Aerenchyma \A`["e]r*en"chy*ma\, n. [NL. a["e]renchyma. See A["e]ro-; Enchyma.] (Bot.) A secondary respiratory tissue or modified periderm, found in many aquatic plants and distinguished by the large intercellular spaces.

n. (context botany English) A spongy, airy tissue found especially in the roots of aquatic plants.

Aerenchyma is a spongy tissue that forms spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root. The channels of air-filled cavities (see image to right) provide a low-resistance internal pathway for the exchange of gases such as oxygen and ethylene between the plant above the water and the submerged tissues. Aerenchyma is also widespread in aquatic and wetland plants which must grow in hypoxic soils.