Scanning Electron Microscopy


Calcium oxalate crystals were observed on facing peridial surfaces of developing basidiocarps of Geastrum minus. Five crystal forms were characterized by their outward shapes and X-ray diffraction patterns: Form One, small bipyramids (COD); Form Two, crystals with split tips (COD); Form Three, crystals with oriented overgrowths (COD); Form Four, large bipyramids (COD); and Form Five, rosettes of plate-like crystals (COM). Forms One and Two were first to appear after peridia separated in unopened basidiocarps, whereas Forms Three, Four and Five were present on exposed peridia of opened basidiocarps. Based on time of appearance during basidiocarp development and crystallography of each form, we believe Form One gives rise to Forms Two, Three and Four. Form Five may arise from dissolution and recrystallization of pre-existing forms. Farinose or asperate basidiocarps of eight other species of Geastrum showed no crystals, indicating that only G. minus forms crystals. Comparison of the five forms with crystals on old basidiocarps indicates Form Four is predominant. The functional value of the crystals is discussed and they are compared with crystal forms found in human and animal urinary tracts.

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