MICROSCOPIC OBSERVATIONS OF THE IRON PLAQUE OF A SUBMERGED AQUATIC PLANT (VALLISNERIA-AMERICANA MICHX)

The immediate interface between the root cell wall and the iron plaque of Vallisneria americana Michx (wild celery), a submerged freshwater plant collected in lakes of the St. Lawrence River system, Quebec, Can ada, was examined. Based on transmission electron microscope observati ons and X-ray diffraction data, the iron plaque of V. americana is com posed mainly of amorphous Fe material (occurring as filaments and disp ersed material) and some crystalline particles (needles and nodules) c omposed of goethite and/or lepidocrocite. Energy dispersive spectrosco py also revealed the presence of Mn-rich particles in the plaque. Impu rities, such as quartz and clays, were present inside the root iron co ating, as were micro-organisms (bacteria) which are postulated to play an indirect role in the deposition of iron oxyhydroxides on the root.