CELL WALL CHEMISTRY AND FINE STRUCTURE IN LEPTOIDS OF DENDROLIGOTRICHUM (BRYOPHYTA): THE END WALL

Leptoids (sieve elements) of Dendroligotrichum are characterized by a highly oblique end wall which is composed of cellulose (birefringent; IKI-H₂SO₄-positive), polyuronides (toluidine blue-positive), pectins (hydroxylamine-positive) and natural aldehydes (silver hexamine and silver proteinate-positive). Cytochemically the end wall appears identical to the unevenly thickened lateral wall. Electron cytochemical localization of aldehydes with silver proteinate reveals two distinct wall layers in comparison to the 3-layered lateral wall. Plasmodesmata are present in the end wall with a frequency of 15-20 per μm². A characteristic feature of end wall plasmodesmata is an expanded median cavity which is 0.12-0.15 μm in diameter. Frequently an electron-dense substance, whose chemical nature and origin are unknown, occludes the plasmodesmata.