The lethal actions in Arabidopsis thaliana and Lemna polyrhiza brought about by certain inorganic form of Mn, Ba, Hg, Cu salts, and organic form of Na salts, were studied with aseptic artificial media. These metal ions at certain concentrations caused lethality of either Arabidopsis or Lemna when the media were without Ca ion. On the contrary, addition of Ca to the media protected the organisms from such lethality. It was postulated for the present from the proceeding evidence that Ca adsorbed and distributed along the sites between the plasma and cell membrane acts for suppressing permeation of toxic level of metal ions causing the lethality of these plants.