SILICON-ACCUMULATING IDIOBLASTS IN LEAVES OF CECROPIACEAE (URTICALES)

A survey of the structure and mineral composition of leaf idioblasts i n the Cecropiaceae was conducted. In all six genera of the family, idi oblasts usually occur as trichomes or enlarged epidermal cells and nea rly always accumulate Si, in marked contrast to the idioblasts of othe r members of the Urticales, which mostly possess cystoliths containing abundant Ca and Si. The horizontally elongate, mineralized structures of Poikilospermum, reported formerly as ''cystoliths'' also contain m ainly Si and little Ca. Six genera of Cecropiaceae share a common char acter in accumulating abundant Si in idioblasts of the leaf epidermis, while lacking cystoliths composed of abundant Ca and Si.