silicon

Symbol: Si. A grey metalloid element, atomic number 14, atomic weight 28. It is not considered essential to plant growth but nevertheless accumulates as silica (Si0₂) in high proportions in the cell walls of some plants. The cell walls of diatoms (Bacillariophyta) are largely composed of silica and certain members of the Xanthophyta and Chrysophyta also accumulate silica. Among higher plants, the stems of Equi-setum are reinforced with silica and the leaves of many grasses also contain substantial amounts. The presence of silica bodies can be demonstrated by carbolic acid solution, which turns such bodies pink. Other crystals remain colourless.