SWEET-CLOVER SEED. 35 



oblique sections showed that the lumina of the Malpighian cells were 

 closed in the region of the light line. Thus it was found that perme- 

 able and impermeable seeds differ mainly in the amount of thickening 

 which occurs in the walls of the Malpighian cells. In the imperme- 

 able 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 imper- 

 meable 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. (PI. 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 be- 

 tween 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. 



No seeds were exposed to the acid for longer than an hour, but at the 

 end of this period the light line was still intact. As compared with 

 other portions of the Malpighian layer, it is extremely resistant to 

 concentrated sulphuric acid. Since all cell walls below the light line 

 are mainly cellulose, the resistance of the light line prevents the acid 

 from destroying the entire seed coat and reaching the embryo. 



