--Longitudinal section of a portion of the grain
of Andropogon Sorghum. x 280 P. Pericarp; Sc. seed-coat; A. aleurone
layer; E. endosperm; S. scutellum; Rs. root-sheath; Rc. root-cap; R.
radicle; Pl. plumule; G. growing point.]

[Illustration: Fig. 21.--A portion of the section of the grain of
Andropogon Sorghum. x 500 P. pericarp; I. seed-coat; A. aleurone layer;
S. starch.]

The caryopsis consists of an embryo on one side at the base and the
endosperm occupies the remaining portion. The embryo can be made out on
the side of the grain facing the glume, as it is outlined as an oval
area. On the other face of the grain which is towards the palea, the
hilum is seen at the base. The grain varies in shape considerably. It
may be rounded, oval, ellipsoidal, narrow and cylindrical, oblong terete
or furrowed. There is considerable variation as regards the colour also.

The =embryo= consists of an =axis= and a =scutellum=. The axis, which is
differentiated into the plumule directed upward and the radicle
downward, is small and straight and it is covered more or less by the
edges of the scutellum. The scutellum is attached to the axis at about
its middle and its outer surface is in contact with the endosperm. This
is an important organ as its function is to absorb nourishment from the
endosperm during germination. The scutellum is considered to represent
the first leaf or cotyledon. The endosperm consists mostly of starch.
Just outside the endosperm and within the epidermis lies a layer of
cells containing much proteid substance. This layer is called the
=aleurone layer=. (See fig. 21.) As an illustration of the caryopsis,
the grain of Andropogon Sorghum may be studied. All the structural
details are shown in fig. 20 which is a longitudinal section of the
grain.

The primary axis of the embryo is enclosed by a closed sheath both above
and below. The sheath which envelopes the radicle is called =coleorhiza=
and that of the plumule, =pileole= or =germ-sheath=.

CHAPTER IV.

HISTOLOGY OF THE VEGETATIVE ORGANS.

The shoots and roots of grasses conform in their internal structure to
the monocotyledonous type. In all grasses numerous threads are found
running longitudinally within the stem and some of these pass into the
leaves, at the nodes, and run as nerves in the blades of the leaves.
These threads are the vascular bundles. The rest of the tissue of the
stem and leaves consists of thin-walled parenchymatous cells o