SILICON IN THE ROOTS OF HIGHER PLANTS

Silicon (Si) distribution in the roots of Sorghastrum nutans (L.) Nash and Sorghum bicolor (L.) Moench. was investigated by means of the electron-probe microanalyzer and scanning electron microscope. In both species, Si was confined to the inner tangential wall of the tertiary-phase endodermal cells in the form of nodular silica aggregates of similar morphology and X-ray intensity. The results are compared to those for six closely related genera, as well as to studies of Si in the roots of species of other tribes of the family Poaceae. The various types of root deposits occurring in the family are described, and their relationships discussed. It is concluded that the type of Si distribution exhibited is determined largely by the phylogenetic status of the genus, rather than by the basic pattern of root anatomy.