Water Relations of the Hemiparasite Rhinanthus serotinus before and after Attachment

Growth of the hemiparasite Rhinanthus serotinus (Schönh.) Oborny was greatly stimulated after attachment of the parasite to the roots of the host plant, Hordeum vulgare L. Before attachment the hydrostatic pressure in the xylem, determined by the pressure bomb technique, was found to be lower in Rhinanthus than in the host. It increased after the formation of haustoria between host and parasite. Apparently, the water transport to Rhinanthus was facilitated. The hydrostatic pressure remained lower than that of the host, accounting for the flow of water and solutes in the direction of the parasite and indicating that there exists a resistance to water transport in the haustoria. Water and solutes were absorbed by the cells, which increased in size. The turgor pressure of the parasite rose steeply, but the osmotic potential was hardly affected.