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

Deposits of silica in the culm internodes, floral bracts andawns of Hordeum sativum Jess (cv Deba Abed) have been investigatedusing the scanning electron microscope The deposits were isolatedfrom all organic matter by digestion with nitric and perchloricacids Two basic types of deposits were recognized, lumen andwall silicification, the latter with or without lumen infillings In the culm internodes, lumen deposits are derived from idioblasts(‘hats’), sclerenchyma and xylem vessels In thefloral bracts they are derived from idioblasts (‘hats’and astenform opals), epidermal long cells (dendriform opals),sclerenchyma and xylem vessels The shape of these deposits doesnot generally resemble the outline of the cell itself, but depositsderived from cell walls do closely resemble the infact cell.In the culm, the walls of stomatal cells, trichomes and, largelythe outer tangential walls of mature long epidermal cells, becomesilicified, together with some cork cells In the floral bracts,silica is found in most epidermal cell walls but is confinedto the trichomes, scutiform cells and costal epidermal cellsearly in their development At maturity concentrations of silicaare much higher in the floral bracts and awns than in the culmsand leaves The results are discussed in relation to the pattern of depositionand its possible functions. Hordeum sativum Jess, barley, silica deposits, opals, scanning electron microscopy