The formation of solid, discrete deposits of opaline silica within the cell lumen of leaf tissues is reported in species representing three subfamilies of the Gramineae; the preparation of a silica-minimal nutrient solution is discussed. Opal phytolith numbers are related to tissue age and to two external silica concentrations for tiller leaves over a period of 32 days following bud initiation. Variations in silica deposition patterns among the individual leaves of a homologous series on the shoot apex are related to differential growth-rates. During ontogeny, deposition occurs in an ordered sequence of cell types related to the basipetal maturation gradient within the leaf. Initial deposition was detected in silica cells (idioblasts) of imbricated, bud leaves of Sieglingia decumbens, 1 mm long; phytoliths are confined to these cells in expanding, basal portions of the leaf. Phytolith counts/sq mm of epidermis vary with the degree of long-cell expansion. The error is reduced by expressing silicification as the number of phytoliths/100 silica cells. Post-expansion deposition was initiated in epidermal long cells of the leaf blade tip. The higher silica concentration resulted in a more rapid utilization of available deposition sites and larger phytoliths (P = 0.001). A passive cell influx of silicic acid is discussed in relation to cytodifferentiation.
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A. G. Sangster (1970) studied this question.