Jan. 20, 1923 Structure of the Pericarp of Johnson Grass Seed 
197 
Their inner walls (d) and side walls (e) are very thick and dense, and 
dark brown in color; their outer walls are much thinner and less dense. 
There is a tendency for the outer walls to collapse into the cell lumen, 
which itself frequently becomes nearly or quite filled with a solidified, 
granular, slightly brown or yellowish mass of substance. 
The outer walls and solidified cell contents are usually difficult to dis¬ 
tinguish from each other. Together they are represented by the cross- 
lined areas (f). 
Toward the distal end of the caryopsis the cells of the inner integument 
gradually increase in size and their inner walls increase in thickness, 
culminating in the great development shown in figure 2 (s). Over the 
embryo the inner integument is much thinner and somewhat lighter- 
colored than over the greater part of the endosperm—a feature which 
largely accounts for the lighter color of the embryo region of the caryopsis 
as contrasted with the endosperm region. The integument decreases in 
thickness also over the flat, or endosperm, side of the caryopsis proxi- 
mally from the position indicated in figure 3, though on this side of the 
caryopsis its inner walls are always thick, dense, and very dark-colored. 
Proximally the inner integument ends in areas of special development 
at the micropyle and the hilum which will be described in detail in the 
following pages. 
Figures 4 to 8, showing specialized areas of the pericarp and inner 
integument of Johnson grass caryopses, were all drawn with camera 
lucida from freezing microtome sections of fully imbibed seeds, the 
sections having first been decolorized on the slide with Javelle water, 
stained with methylene blue, and mounted in 75 per cent glycerin solu¬ 
tion. The decolorizing process entirely removed the solid contents of 
the integument cells and somewhat increased the size of all cells. As 
the aleurone layer usually remained attached to the inner integument 
in the sections even when nearly all of the endosperm fell out, this 
layer is shown in the figures representing areas where it is present. 
PERICARP AND INNER INTEGUMENT AT THE DISTAL END OF THE CARYOPSIS 
Figure 4 represents a median sagittal section through the coverings of 
a Johnson grass caryopsis at its distal end. The inner integument (a) 
is much thicker than the combined thickness of the pericarp and the 
aleurone layer, and is much thicker toward the flat (endosperm) side 
of the caryopsis (A) than toward the embryo side (B), though this 
relatively great difference does not persist far from the distal end. The 
inner walls of the integument cells (1) are extremely thick and bear at 
intervals peculiar knoblike ingrowths (2) into the cell cavity. These 
ingrowths may be smooth but more frequently are studded with minute 
points. In the latter case, very infrequently one is found which before 
bleaching with Javelle water, but never after bleaching, exhibits double 
refraction in polarized light as if crystalline in structure. These ingrowths 
occur only near the distal end of the caryopsis. The long cells of the 
integument at the extreme distal end of the caryopsis sometimes extend 
far into the style and are broken off with the style by rough handling 
of the caryopsis. The relatively thin end walls of the integument cells 
at a little distance from the distal end are sometimes slightly folded (3) 
as if from the inward pressure of the pericarp, as it dries during matura¬ 
tion of the caryopsis. 
