203 
jan. ao, i 9 23 Structure of the Pericarp of Johnson Grass Seed 
slender. The glumes are more fragile and more easily broken or removed, 
so that commercial lots of Sudan grass seed usually contain a considerably 
larger percentage of hulled caryopses than do Johnson grass seed. The 
caryopses are lighter colored, less glassy in appearance, and are more 
easily injured mechanically. The coat structures usually form con¬ 
spicuous delicate folds or creases over the axial organs of the embryo, 
as the embryo shrinks during maturation and drying, while in Johnson 
grass caryopses the coverings are stretched rather tightly over the 
embryo even after the caryopsis is fully dried. In a Johnson grass 
caryopsis the micropylar prominence is usually the most proximal part 
of the inner integument, the embryo not extending farther forward 
than the micropyle. In a Sudan grass caryopsis, on the contrary, the end 
of the radicle and of 
the scutellum usually 
extend farther forward 
so that the inner in¬ 
tegument is strongly 
arched forward from 
the micropyle to cover 
these organs. The 
Sudan grass embryo 
is therefore more ex¬ 
posed to mechanical 
injury than the John¬ 
son grass embryo. 
The micropylar 
structure is frequently 
less massive in Sudan 
grass caryopses than 
in Johnson grass cary¬ 
opses. An open micro¬ 
pyle is rare in Johnson 
grass and somewhat 
more common in Sudan 
grass. One Sudan 
grass caryopsis was 
examined which had a nearly circular micropylar opening somewhat 
more than ioo microns in diameter through the integument. 
Many Sudan grass caryopses are very light colored, and occasionally 
one is found which is almost white. . In some such light colored caryopses 
the inner integument is poorly developed or almost lacking. In others 
it is as well developed as in the dark colored caryopses, but is less pig¬ 
mented. Johnson grass produces no such light colored caryopses, and 
the inner integument is always well developed. Its thick inner wall, 
as well as the pericarp tissue, is more darkly pigmented than in Sudan 
grass caryopses. 
measurements or coat structures 
Since removal of the coverings over the embryo of Johnson grass 
caryopses removes the restrictions to their germination at moderate and 
constant temperatures and makes them capable of germinating vigor¬ 
ously under the same conditions as Sudan grass caryopses, it was thought 
desirable to compare these coverings in the two kinds of seed. Measure¬ 
ments were therefore made of the minimum thickness of the coat 
Rig. io. —Internal view of the hilar orifice of a Johnson grass caryopsis 
4 with its “dosing tissue:” a, ends of the integument cells; b, “closing 
tissue;” c, margin of the hilar orifice; the arrow points in the direc¬ 
tion of the micropyle. X 180. 
