202 
Journal of Agricultural Research 
Vol. XXIII, No. 3 
Fig. 8.—Median sagittal section through a Johnson grass 
caryopsis, partially bleached to show the “closing tissue'’ 
over the hilar orifice: a, embryo; b, endosperm; c, c, c, inner 
integument; d, micropyle; e, hilar margins; f, “closing tis¬ 
sue;” g, traclieids from the pedicel. X 27. 
with Javelle water. After the surrounding cells are almost completely 
decolorized, the compact, densely pigmented central portion, the “closing 
tissue,” still remains very dark, with the individual cell walls wholly 
indistinguishable. Figure 8 represents in outline a median sagittal 
section of a Johnson grass caryopsis which had received this partial 
bleaching with Javelle water. On further treatment with Javelle water 
the cell walls in this dark 
closing tissue (f) also become 
completely decolorized and 
the compressed cells resume 
their cubical shape as shown 
in figures 6 and 7. 
The relation of the clos¬ 
ing tissue of the hilum to 
the integument cells is fur¬ 
ther shown in figures 9 and 
1 o. The material from which 
these figures were drawn was 
from seeds which had been 
treated with 50 per cent 
chromic acid until the outer 
layers of the pericarp, the coverings of the embryo, the proximal end 
of the embryo itself, and the pericarp tissue within the hilar orifice 
had been dissolved away. This left in the hilar region only the more 
resistant integument and “closing tissue.” These were removed with 
a sharp scalpel, bleached, washed and stained upon the slide, and 
mounted in 75 per cent glycerin with thin strips of tissue paper under 
the cover glass to protect the 
now extremely delicate struct¬ 
ures from crushing. The fig¬ 
ures show only one cell layer 
of the closing tissue, which is 
really several cells thick. 
Figure 9 is an external view 
with the underlying margin of 
the hilar orifice shown as a con¬ 
tinuous heavy line (a). The 
drawing was made with camera 
lucida and represents accu¬ 
rately the loose ends of the 
cell walls (b) at the margin of 
the tissue which had resisted 
the corrosive action of the 
chromic acid. 
Figure 10 is a view’ from the 
inner side of the hilum, looking out. The ends of the out-curving 
integument cells (a) present a stereoscopic appearance, while the much 
thinner-walled closing tissue (b) is shown in a lower focal plane as it 
appeared through the hilar orifice. 
Fig. 9 — External view of the “closing tissue” over the hilar 
orifice of a Johnson grass caryopsis: a, underlying hilar 
margin; b, loose ends of cell walls of the “closing tissue,” 
beyond which the tissue was destroyed by chromic acid; 
the arrow points in the direction of the micropyle, X 180. 
COMPARISON OP JOHNSON GRASS AND SUDAN GRASS FRUITS AND CARYOPSIS 
Sudan grass seed differs from Johnson grass seed in certain minor 
ways, some of which, however, are physiologically important. Both the 
unhulled fruits and the caryopses are slightly larger, flatter, and more 
