200 
Journal of Agricultural Research voi. xxiii, no. 3 
Under the micropyle is a group of large empty functionless endosperm 
cells (s) which continue also under the hilum and gradually give place 
to the starchy reserve cells of the endosperm. 
the hilum 
Since in a caryopsis the seed never becomes detached from its peri¬ 
carp there is, of course, no true hilum, or seed scar. There is, however, 
in tiie caryopsis of the Andropogoneae, a large opening through the inner 
integument in the position corresponding to the hilum. Figure 6 repre¬ 
sents this hilar orifice of a Johnson grass caryopsis in median sagittal 
section and figure 7 in median transverse section. 
The cells of the inner integument are slightly turned outward at the 
margins of the hilar orifice (a, a). The group of small, compact, thick- 
walled, pigmented, pericarp cells mentioned in the preceding section are 
Fig. 6. Median sagittal section through the hilar orifice of a Johnson grass caryopsis: A, side toward 
micropyle and endosperm; B, side toward embryo, showing inner integument (a, a), compact group 
of thick-walled pericarp cells (b, b), “closing tissue” of the hilar orifice (c), outer epidermis of the peri¬ 
carp (d), pericarp cells completely filling the hilar orifice in the integument (e). X 275. 
present outside of the margins of this orifice on all sides (b, b). They are 
particularly prominent in sagittal section on the side toward the micro- 
pyle (fig. 6, A) and are rather sparingly represented on the embryo side 
(fig. 6, B). Ninety degrees around the circumference of the hilar orifice 
from these points as shown in figure 7, they are very numerous, but not 
as thick-walled as at the longitudinal extremities of the hilar region. 
Stretching over this region from the points where these thick-walled 
pericarp cells fuse with the integument near the margins of the hilar 
orifice is a continuous stratum of several layers of pericarp cells with 
somewhat thickened walls (c), which, though forming a single tissue with 
the cells on both sides of them, differ from these in ways which are of 
great physiological significance. The radial contraction which charac¬ 
terizes all pericarp tissues in the dry, mature caryopsis, causing the very 
noticeable hilar depression, apparently reaches its maximum in this 
stratum, which also becomes intensely pigmented with a dark brown 
pigment and, with the thick-walled cells shown at b, b, forms a pro- 
