Cells were fixed in 2.5% glutaradehyde in 0.1 M phosphate buffer, pH 7.2 (containing 6% sucrose wt/ vol) for 24 h at 25 C and then washed in the same buffer containing 12% sucrose (wt/vol). The specimens were freeze dried. Dried specimens were coated with gold and examined in a model JSM 25 S scanning microscope (Jeol Ltd., Japan) at an accelerating voltage of 15 kV.