Electron-probe Microanalysis Studies of Silicon in the Epicarp Hairs of the Caryopses of Hordeum sativum Jess., Avena sativa L., Secale cereale L. and Triticum aestivum L.

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Abstract
Silicon deposits in the epicarp hairs of the caryopses of mature, field-grown specimens of Hordeum sativum, Avena sativa, Secale cereale and Triticum aestivum were investigated using electron-probe microanalysis. In all four cereals, silicon was most concentrated at the extreme tips of the hairs. In barley, it was the only element detected; in the other three cereals potassium and calcium were located below the tip. In wheat, chlorine was also detected. The hair bases of the different cereals displayed variation in the elements detected. Silicon and polassium were present in all four and calcium present in all except rye. The hair bases of wheat also contained chlorine; phosphorus and zinc were located in barley. The latter alone showed variation of elements between hair bases. Scanning electron microscopy revealed heavy striations of the hair tips of barley and oats. In rye and wheat, the tips were smooth but there were slight surface markings below the tip. The results are discussed in relation to the possible functions and significance of the epicarp hairs and their silicification.