A Developmental Study of Silicification in the Trichomes and Associated Epidermal Structures of the Inflorescence Bracts of the Grass, Phalaris canariensis L

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Abstract
Silicon accumulation is greatest in the abaxial epidermis of the inflorescence bracts of Phalaris canariensis L. It occurs initially in glumes 1 week before emergence, at low levels in the trichomes and long cells, but at high levels in the papillae. Accumulation in long cells remains low throughout, although it increases with time. Papillae and prickle hair silicon counts considerably exceed values for other epidermal structures. Silicon is also deposited in glume macrohairs before emergence, and at maturity reaches intermediate levels. Little silicon is present in the macrohairs and long cells of the abaxial epidermis of the fertile lemma prior to emergence. After emergence, however, silicon is rapidly accumulated in these structures, and at maturity they have the highest silicon levels of all the mature bract tissues. Silicon accumulation in the lemma lags behind that of the glume until emergence, when it increases more rapidly, and by maturity exceeds that of the glume in macrohairs and long cells. The significance of the results is discussed in relation to wall thickening, bract anatomy and panicle emergence.