... form in the substance of the cell wall. In addition to this, crystals of mineral matter, having various shapes and sizes, are often found in the interior of cells. The most common of these interior cell crystals are those composed of calcium oxalate and calcium carbonate. Others composed of calcium phosphate, calcium sulphate and silica are sometimes found. These crystals may occur singly or in clusters of greater or less size. In shape they are prismatic ... — Popular Science Monthly Volume 86
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