An Ultrastructural Study on the Developmental Phases and Silicification of the Glumes of Phalaris canariensis L.

In the glume of Phalaris canariensis L. silicon deposition takesplace in the macrohairs, papillae, prickle hairs and silicacells of the abaxial epidermis before panicle emergence. Early in their development the macrohairs have large vacuolesand thin walls. At maturity the walls become thickened and aremajor sites of silica deposition. Dry ashing reveals a helicalpattern within the hair walls. Distinct papillae and prickle hairs were first observed oneweek before panicle emergence. Here silicification was initiallyconfined to outer tangential walls, but by two weeks after emergencetheir cytoplasmic contents had broken down, and the lumina werefilled with siliceous granules. Cork-silica twin cells werealso present in the abaxial epidermis. By panicle emergencethe silica cells were infilled, but the cork cells retainedtheir cytoplasmic contents. The long cells of the abaxial epidermiswere initially thin walled, but thickening occurred in the outertangential wall, this being complete by one week after emergence.These cells remained relatively unsilicified throughout. After panicle emergence the adaxial epidermal cells, and theirassociated parenchyma cell layers began to lose their cellularcontents and collapse. This process was complete two weeks afteremergence when the collapsed walls formed a thin internal layerbetween the two epidermi. Electron opaque granular material,containing several elements, but predominantly calcium, waspresent between the collapsed cell walls. The results are comparedwith those for the lemma, and silica deposition mechanisms arealso discussed. Phalaris canariensis L., canary grass, silicification, trichome, glume, ultrastructure