Endodermal Silicification in Mature, Nodal Roots of Sorghum bicolor (L.) Moench.

Nodal roots of mature, soil-grown specimens of Sorghum bicolor(L.) Moench. were investigated for their Si content by meansof the electron-probe microanalyser and the scanning electronmicroscope. No consistent accumulation of Si occurred other than in theendodermis. Indication of a lower Si content in the old as comparedto the younger nodal roots was obtained. The solid silica depositsoccurred as domeshaped silica aggregates confined to the innertangential wall. Comparisons with the similar deposits of youngseminal roots are made. It is argued that the endodermal deposits represent a specializedaspect of silicification and contrasting hypotheses to accountfor it are proposed, one involving physico-chemical factors,the other, protoplasmic control.