Formation of Perforation Plates and Bordered Pits in Differentiating Vessel Elements

Abstract

Disintegration processes of end walls and pit membranes in later stage of maturation of the vessel elements were observated with electron and optical microscopes using a poplar tree (Populus nigra L. var italica KOEHNE). The major components of the end walls may be disintegrated enzymatically from their surfaces, but disintegration of the minor components (probably a part of cellulose micro-fibrils) may be achieved by the transpiration streams. In the case of intervessel pit membranes, it seems that only the non-cellulosic substances may be removed enzymatically. Parenchyma cells adjacent to vessels, having protective layers, seem to be got rid of the enzymatical attack through the vessel-parenchyma pit membranes. Considering the observation results by O'BRIEN (1970), it seems likely that the disintegration of unlignified cell walls is a general phenomenon that occurs later in the autolysis of the vessel elements.