Scanning Electron Microscopy of Silica Deposits in the Culms, Floral Bracts and Awns of Barley (Hordeum sativum Jess.)

Abstract

Deposits of silica in the culm internodes, floral bracts and awns of Hordeum sativum Jess (cv Deba Abed) have been investigated using the scanning electron microscope The deposits were isolated from all organic matter by digestion with nitric and perchloric acids Two basic types of deposits were recognized, lumen and wall silicification, the latter with or without lumen infillings In the culm internodes, lumen deposits are derived from idioblasts (‘hats’), sclerenchyma and xylem vessels In the floral bracts they are derived from idioblasts (‘hats’ and astenform opals), epidermal long cells (dendriform opals), sclerenchyma and xylem vessels The shape of these deposits does not generally resemble the outline of the cell itself, but deposits derived from cell walls do closely resemble the infact cell. In the culm, the walls of stomatal cells, trichomes and, largely the outer tangential walls of mature long epidermal cells, become silicified, together with some cork cells In the floral bracts, silica is found in most epidermal cell walls but is confined to the trichomes, scutiform cells and costal epidermal cells early in their development At maturity concentrations of silica are much higher in the floral bracts and awns than in the culms and leaves The results are discussed in relation to the pattern of deposition and its possible functions.