ery there is a single layer of cells called the =pericycle=. The
arrangement of the xylem and the phloem is different from that of the
stem. They lie side by side on different radii, and not one behind the
other on the same radius as in the stem. The number of xylem groups is
fairly large and the development of the xylem is from the pericycle
towards the centre of the stele. (See figs. 44 and 45.) The
parenchymatous cells in the centre of the stele become thick-walled in
older roots.

=Structure of the leaf.=--The structure of the leaf of grasses is quite
characteristic of the family. In every leaf a number of vascular
bundles, some small and others large, pass from the base to the apex.
Externally the leaf is covered on both the sides by the epidermis. The
spaces existing between the vascular bundles and the epidermis are
filled with parenchymatous cells. The larger vascular bundles consist of
xylem and phloem surrounded by a bundle sheath of a single layer of
cells. In the smaller bundles the xylem is very much reduced. Around
every vascular bundle there is a single row of somewhat large cells
densely packed with large chloroplasts, the =chlorophyllous layer=. The
vascular bundles are strengthened by fibres, on both the sides in the
case of larger bundles and on only one side in small bundles.

[Illustration: Fig. 47.--Transverse section of the stele portion of the
root of Andropogon Sorghum. x 150

Co. Cortex; en. endodermis; pe. pericycle; ph. phloem; pr. protoxylem;
xy. xylem vessel.]

[Illustration: Fig. 48.--A portion of the transverse section of the leaf
of Panicum javanicum. x 100

Ep. c. An ordinary epidermal cell; st. stomata; sc. sclerenchyma; ph.
phloem; chl c. chlorenchyma; m. motor cells; xy. xylem.]

For a detailed study of the structure of the leaves of grasses the leaf
of the grass _Panicum javanicum_ may be chosen. In a transverse section
of this leaf, the vascular bundles are very conspicuous. The larger
bundles are normal in every way, while in the smaller ones the xylem
elements are considerably reduced. Around every one of the vascular
bundles there is a single row of large cells containing large
chlorophyll grains (the chlorophyllous layer). In a well developed large
vascular bundle the chlorophyllous layer is open below just close to the
sclerenchymatous band. On both sides of the larger vascular bundle there
are bands of sclerenchyma. In the case of smaller bundles some are
strengthened