In the coats of the impermeable seeds the light line was usually broader, the Malpighian cells thickened more below the light line, and the main cavities of the Malpighian cells were more reduced and farther below the light line than in the coats of permeable seeds. (Pl. V, fig. 6.) No canals except occasionally a few very small ones were seen crossing the light line in impermeable seeds. Cross and oblique sections showed that the lumina of the Malpighian cells were closed in the region of the light line. Thus it was found that permeable and impermeable seeds differ mainly in the amount of thickening which occurs in the walls of the Malpighian cells. In the impermeable seeds the thickening which begins at the outer tangential wall of the Malpighian cell extends farther toward the inner tangential wall, leaving the cell lumina smaller and farther below the light line than in permeable seeds. The thickening is also more complete in impermeable seeds, leaving fewer and smaller canals across the light line as well as closing the cell lumina in the region of the light line. THE ACTION OF SULPHURIC ACID ON THE COATS OF IMPERMEABLE SEEDS. Impermeable seeds were soaked in concentrated sulphuric acid (sp. gr. 1.84) for 15, 30, and 60 minutes; then washed and put in the staining solutions. After they had swollen, they were removed from the staining solutions, dried, and embedded in glycerin gum. A study of these seeds showed that the acid had eaten away all of the material outside of the light line and that the stain had passed through all regions of the seed coat. (Pl. V, fig. 10.) When observed under the microscope, it was seen that the action of the acid was rapid, destroying the cuticle, cuticularized layer, and cones in about 5 minutes. After 15 minutes treatment with acid the light line, aside from the presence of canals and pores not previously visible, seemed to be very little affected. The division lines along which the lateral walls of the Malpighian cells were joined now became much more distinct across the light line, thus indicating that there was some swelling in this region. When a close examination of the path of the stain was made the cell lumina, and occasionally very small pores, were found to extend across the light line. The presence of the stain in the pores indicated that they were paths of the stain across the light line. Some of the stain passed along the lines between cells and through the occasional canals crossing the light line, but judging from the intensity of the stain in the lumina the canals appeared to be the principal passageways. The action of the acid in opening the cell cavities across the light line was not determined. It may be due to the swelling of the light line or to the removal of substances closing the pores.