24 Jackson. — Anatomical Structure of the Roots of Barley. 
Anatomy of Branched Roots. 
pilife ro us layer:: 
Young roots. A transverse section of a young barley root examined 
seven days after sowing, when the root was about i in. in length, presents 
the appearance shown in Fig. 2 . The middle of the root is occupied by 
a kind of duct bordered by thin-walled cells. The endodermis bounding 
the stele is distinguishable as a row of tangentially elongated cells, with 
their walls as yet unthickened. Immediately within the endodermis lies the 
pericycle, consisting of radially elongated cells, the continuity of which is 
broken opposite each 
of the seven xylem 
groups, where the 
protoxylem elements 
abut directly on the 
endodermis. In addi- 
tion to the smaller 
cells of the proto- 
xylem each xylem 
group contains one 
large vessel. Alter- 
nating with the xylem 
arethephloem groups, 
the cells of which are 
at this stage not easily 
distinguishable from 
the rest of the thin- 
walled ground tissue. 
Outside the endo- 
dermis are four to six 
layers of large thin- 
walled cortical cells, bounded by the piliferous layer. The endodermis and 
all the tissues within it consist of cells packed tightly together, so that no 
intercellular spaces occur. The same is true for the piliferous layer, but in 
the cortex small spaces do occur between the cells. These spaces are not 
entirely due to shrinkage as they are found in fresh material. 
Intermediate stage between a young and an old root. A root slightly older 
than that shown in Fig. 2 shows essentially the same structure, the chief 
difference being in the pericycle and endodermis, where the cells show signs 
of thickening. In the pericycle this thickening affects the whole cell wall, 
but in the endodermis it affects chiefly the inner and radial walls, and it is 
most noticeable in the cells lying in the zone between the xylem groups. 
This seems to suggest the formation, at least in the comparatively young 
roots, of passage cells, as described for Allium and various other plants by 
TS : Young branched root, fxioj) 
Fig. 2. 
