The barley root (Hordeum vulgare) of 3-day old seedlings were treated with potassium oxalate to study the distribution of calcium among plant cell organelles. The best results were obtained by previously treating the root with 10(-3) M CaCl2 followed by an incubation for 20 min with potassium oxalate. The unstained sections for electronmicroscopy showed the deposits of calcium oxalate as a granular or a dark layer on the mitochondria, endoplasmic reticulum and the nucleare envelope. Within all the cells, dark bodies, like vacuoles, were noticed.