ran. 20,1923 Structure of the Pericarp of Johnson Grass Seed 
195 
II. INTERNAL STRUCTURE OF THE CARYOPSIS 
A large number of botanists have investigated the embryos of various 
grasses. Several of these, among whom are Bruns (8), Pammel (26), 
Guerin (14), Kennedy (19), and Sargant and Arber (27), have described 
the embryos and other organs of the caryopses of species of Andropogon, 
Sorghum, and other species of the tribe Andropogoneae. 
Figure 2 shows a median sagittal section of a Johnson grass caryopsis. 
No attempt is made here to distinguish between integument and pericarp, 
as these structures are discussed and illustrated 
in later sections. 
Besides the axial organs, the rather large 
embryo (A) includes the scutellum (a), the root 
sheath, or coleorhiza (i),and theepicotyl sheath, 
or coleoptile (k). The radicle (g) is directed 
toward the proximal end of the caryopsis. Its 
tip is covered by a well-developed root cap (h). 
The epicotyl (f), with the first two convolute 
leaves (x 1 and x 2 ) well formed and the rudi¬ 
ments of later leaves, extends toward the distal 
end of the caryopsis. Between the radicle and 
the epicotyl is a short, internode-like structure, 
the mesocotyl (e), which is variously inter¬ 
preted as the fused hypocotyl and stalk of 
the cotyledon (27) or the elongated primary 
node (31). 
The scutellum is expanded laterally into two 
wings which fold up around and almost wholly 
envelop the axial organs of the embryo. A 
section of the upper edge of one of these wings 
is shown at (d). Wherever the scutellum is in 
contact with the endosperm (B) the cells of its 
lower cell layer are elongated into the form of 
a columnar epithelium (b), which secretes 
diastase and possibly other enzyms for the con¬ 
version of the stored food’ of the endosperm. 
Along the entire length of that portion of the 
scutellum underlying the mesocotyl and epicotyl 
extends a central procambium strand (c), which 
enters the axial organs at the point of their 
insertion upon the scutellum and which sends 
off about a dozen small lateral branches and a short branch which 
extends under the radicle. These branches ramify throughout that face 
of the scutellum which is in contact with the starchy endosperm. Upon 
the germination of the caryopsis the elements of the central strand become 
differentiated, with the formation of spiral tracheae, and the cells of the 
columnar epithelium greatly elongate. These morphological changes can 
also be induced by wounding the endosperm region of the caryopsis or by a 
diseased condition of embryo or endosperm. The elongation of the 
epithelial cells, either generally over the whole face of the scutellum or 
locally, is always accompanied by corrosion of the starch grains in the 
underlying endosperm cells. 
Just inside the coverings of the caryopsis (m) and extending entirely 
around the embryo and endosperm except at the region of the hilum and 
Fig. 2.— Median sagittal section of 
a Johnson Grass caryopsis: A, 
embryo; B, endosperm, showing 
scutellum (a), its epithelium (b), 
its central procambium strand 
(c), portion of wing of scutellum 
rolled up over the axial organs of 
the embryo (d), mesocotyl (e), 
epicotyl with its embryonic 
leaves X 1 and X* (f), radicle 
(g), root cap (h), root sheath or 
coleorhiza (i), epicotyl sheath or 
coleoptile (k), aleurone layer (1), 
fused pericarp and seed coat (m), 
remnant of style (n), pedicel with 
remnants of lodicules (o), region of 
the hilum and micropyle (p) .com¬ 
pressed and empty endosperm 
cells (r), and elongated distal cells 
of the integument (s). X 25. 
