SCIMAT / SCIENCE PHOTO LIBRARY SCIMAT / SCIENCE PHOTO LIBRARY
Calcium oxalate bipyramidal crystals on the leaf of rhubarb (Rheum rhabarbarum), just above a stoma in the left half of the image. Small leaf fragments were fixed in glutaraldehyde in the presence of calcium acetate, dehydrated in ethanol, and critical-point dried for SEM. Large quantities of calcium oxalate are found in the poisonous plant dumbcane (Dieffenbachia). It is also found in rhubarb leaves, various species of Oxalis, Araceae, and agaves, and (in lower amounts) in spinach. Nonsoluble calcium oxalate crystals are found in plant stems, roots, and leaves. Calcium oxalate crystals in the urine are the most common constituent of human kidney stones, and calcium oxalate crystal formation is also one of the toxic effects of ethylene glycol poisoning. Solubility in water: 0.00067 g/100 ml (20C). Enhanced SEM. Image width: 25.6 micrometers. Magnification: 3905x if the image is printed 10 cm wide.
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