Absorption and accumulation of calcium in hydro— ponic solutions, deficient or not in calcium, are studied on whole plants of Sorghum (Sorghum dochna F.), In deficient lots, calcium is replaced either by magnesium (Ca/Mg lot), or by potassium (Ca/K lot). The limit threshold of defiency retained, does not modify, on the 26 day of culture (end of the experience) the yield of different lots compared with the control. The principal modifications in cation content are noted in leaves: plants grown in the Ca/Mg solution show a higher Ca content than plants in a Ca/K solution. As a consequence of saturation with potassium the substitution of Ca in the two deficient lots is effected by magnesium.