WATER-CONDUCTING CELLS OF EXTANT SYMPHYOGYNA-TYPE METZGERIALEAN TAXA - ULTRASTRUCTURE AND PHYLOGENETIC IMPLICATIONS

An EM-reinvestigation of the water-conducting cells (''hydroids'') in the liverwort genera Hymenophyton, Pallavicinia, Podomitrium and Symph yogyna, in relation to the water-conducting cells recently described f or early land plants, revealed a uniform structure. The cell wall cons ists only of the middle lamella and the homogenous unlayered primary w all. Most of what were previously presumed to be perforations are of a secondary nature, due to ruptured middle lamellae. There are only few really genuine perforations. The water-conducting cells correspond ne ither with the S-cell type of Silurian/Devonian Rhyniophytina nor with the G-cell type of the same-aged Zosterophyllophytina. Both cell type s are to be excluded as possible ancestors of the water-conducting cel ls of extant Symphyogyna-type Metzgerialean taxa.