Internal segmentation of rhizomes of Phragmites australis: protection of the internal aeration system against being flooded

Segmentation of the aeration system and its anatomy was studied in rhizomes of common reed (Phragmites australis). Segmentation is achieved by nodal d iaphragms which allow the passage of pressurised gas-few but which also for m effective barriers against flooding of the internal space in case of loca l injury. The pressures required to force water through the diaphragms were measured and compared with the anatomical structure of the diaphragm. The fine hydrophilic stellate parenchyma of the diaphragms was shown to act as a matrix supporting menisci of air-water interfaces and therefore preventin g water movement until the 'limit' pressure (measured values ranged from 18 to >40 kPa) was overcome. Although the surfaces of the large stellate pare nchyma and sclerenchyma strands covering the diaphragm are hydrophobic thes e components do little to prevent the ingress of water.