FLANGE-TYPE PARENCHYMA TELLS - OCCURRENCE AND STRUCTURE IN THE HAUSTORIUM OF THE DWARF MISTLETOE KORTHALSELLA (VISCACEAE)

Range cells are an unusual type of parenchyma cells with an open retic ulate pattern of secondary wall thickenings. The cells superficially r esemble tracheary elements but are otherwise fundamentally different. Range cells were found in haustorial sucker tissue of the dwarf mistle toe Korthalsella. Such cells were previously unknown for a mistletoe, or other parasitic angiosperm. Flange cells are confined to the xylem of the sucker and occur as either diffuse aggregates amongst the ordin ary parenchyma tissue lying between the tracts of vessels, or abut the vessels. Typical flange cells are absent at the parasite/host xylem i nterface. The cells contain a well differentiated protoplast, includin g chloroplasts with extensive granal stacks. Histochemical staining an d fluorescence microscopy indicate lignification of the flange wall. I n thin section, the flange wall is often stratified into dark and ligh t staining layers. Flange cells in Korthalsella resemble contact cells , vessel associated cells and certain types of transfer cells reported in the literature. Based on morphological considerations, it is sugge sted that flange cells in Korthalsella are involved in absorption and transport between host and parasite. As host sap moves through the suc ker apoplasm, substance might be selectively absorbed by the flange ce ll, before the remaining the sap passes into the vessels for long dist ance transport in the mistletoe.