The effect of several inorganic forms of calcium on cotton (Gossypium hirsutum L.) seed radicle growth (measured in length) at a suboptimal temperature was evaluated 14 days after imbibition onset. Cotton seed were imbibed in rolls of germination paper placed upright in Styrofoam cups filled with calcium solutions of various concentrations. Experiments were performed using a closed air-circulation system incubator at 15 C. Solutions of calcium nitrate and calcium chloride (0.625 to 10 mM) stimulated radicle growth at 15 C up to 106 and 158%, respectively. Similarly, mean radicle growth of cotton seeds imbibed in 10 mM calcium sulfate was 129% greater than those imbibed in 0.078 mM calcium sulfate. Radicle growth of distilled water controls for calcium sulfate experiments, however, was stimulated to a level 181% greater than that achieved when seed were imbibed with 0.078 mM calcium sulfate. This anomalous stimulation of water controls was repeated in additional experiments using sealed, 4-liter chambers which enclosed seed rolls moistened with distilled water placed physically adjacent to open solutions of calcium and magnesium sulfate. Radicle growth at 15 C of cotton seed imbibed in water was stimulated 50 and 65% when adjacent to solutions of 0.313 and 0.625 mM calcium sulfate, respectively, relative to when they were adjacent to water alone. Similarly, in the sealed chambers, a solution of 0.313 mM magnesium sulfate stimulated radicle growth of seed imbibed in water 80% over an adjacent open solution of water alone. Concentrations of calcium sulfate that were effective at 15 C, failed to stimulate radicle growth of seed imbibed in water at 32 C when growth measurements occurred three days after imbibition onset.