The dry weight percentages of BaS04 in Spirogyra, reported in an earlier, preliminary paper were corrected and determined at 0.4-0.7 %. Electron microscopy has shown that the BaSG4 is present in the protoplasm and not in the cell wallt. It has the form of individual, mainly rectangular prisms, the majority of which is about 0.3 p. long with an average width about 0.17 p and variations in size ranging up to about 0.9 x 0.48 p. Presumptive evidence has indicated as their face of greatest extension the crystallographic plane containing the unit cell axes a = 8.87 A and b = 5.45 A. Generally, they occur at wide inter-distances, and as far as the material allowed to be concluded, mainly in the periphery of the cytoplasm. On the basis of the dry-weight content and crystallite size an estimation has been made of the distance between the crystallites in case of an even distribution in the living cell and of the degree of accumulation of BaS04 in the latter. The crystallites were found to be visible under the polarizing microscope.