EVIDENCE FOR THE ESSENTIALITY OF SILICON FOR GROWTH OF THE BEET PLANT

In experiments as yet unpublished, difficulty was encountered in growing plants of the Detroit Dark Red variety of the table beet (Beta vulgaris L.) in culture solutions of low concentration in asphalt-painted iron containers. When the plants were transferred from solutions made with a distilled water contaminated with tap water to solutions made with uncontaminated distilled water, the plants in lower concentrations of nutrient salts wilted badly within a few days after being transferred, and the roots became dark in color. Those in higher concentrations made satisfactory growth, which suggested the possibility that some necessary element was being supplied as an impurity in the C.P.^grade chemicals. Preliminary experiments with varying quantities of the four chemicals employed in making the solutions indicated that the impurities might be contained primarily in the ammonium phosphate. Since A5 (B, Cu, ??, ??, Mo) and B6 (Ti, V, Cr, W, Co, Ni) chemicals2 had been supplied, it was thought possible that the missing nutrient might be one contained in the C13 mixture used by Arnnon (1) (Al, As, Cd, Sr, Hg, Pb, Li, Rb, Br, I, F, Se, Be). Single plants from the concentrated solutions were transferred to Mason jars coated with a thin layer of asphalt paint and containing nutrient solutions one-half as concentrated as those used by Arnon. The plants were supplied with various combinations of the 13 micro-elements. Others received small quantities of sodium, chlorine, and increased quantities of B, Cu, Mn, Zn, V, Cr, W, Co, and Ni. The solutions were not aerated. After a few days the plants wilted irrespective of treatment. The possibility existed that beet plants might have a high requirement for oxygen in the solution and for that reason these plants were kept for comparison with those grown in metal containers in aerated solutions. After 3 weeks the roots of the plants in the Mason jars were making good growth and were lighter in color than any of those in the metal containers. This observation suggested that some nutrient was dif-