A manual of rice seed health testing - IRRI books - International Rice ...

nous structure called the ligule,
which may be glabrous or ciliate. Its
size, color, and shape vary among
varieties.
The number of leaves in the main
culm is always greater than the
number of tillers. The number decreases
from the primary to the tertiary
tillers. The prophyllum is at the
base of the main tiller.
Floral organs. The rice plant terminates
in an inflorescence (blossom,
flower) called a panicle. Each unit of
the inflorescence is a spikelet.
—The panicle (Fig. 2.4) grows
from the uppermost internode. The
upper extremity of the uppermost
internode, where primary branches
of the panicle arise, is called the
panicle base or neck. The axis starting
from the panicle base to its end is
the primary panicle axis. It is differentiated
into nodes and internodes.
The nodes are solid; the internodes
are fistular. In the axils of branches
on the panicle are swollen portions
called panicle pulvini. Each node
gives rise to primary branches,
which in turn bear secondary
branches. The secondary branches
bear the spikelets.
—Varieties vary greatly in panicle
length, shape, insertion angle of primary
branches, and weight and density.
—The spikelets (Fig. 2.5) are
pedicelate. They have a short axis
called the rachilla. The flower is
borne in the axil of two types of
bracts. The first pair of bracts are
sterile, and are known as sterile lemmas
(glumes, empty glumes, or
outer glumes). These may be of unequal
size, and are generally smaller
than the fertile glumes. The upper
pair of bracts is called the fertile
(flowering) glumes and consists of
lemma and palea. The glumes
(lemma and palea) and the floral organs
constitute the floret.
2.4 The panicle.
2.5 The spikelet
and flower.
The lemma is a five-nervcd bract
partly enveloping the smaller threenerved
bract palea. The middle
nerve or keel may be hairy or
smooth. These bracts extend into
smaller structures called apiculi. The
apiculus at the lemma is known as
the lemmal apiculus while that at the
palea is the paleal apiculus. The
lemma may also bear an awn, which
is the extension of its keel. The surface
of the bracts may be smooth or
hairy.
—The flower (Fig. 2.5) is bisexual,
complete, hypogynous, and
zygomorphic.
—The perianth (Fig. 2.5) is modified
and greatly reduced into two
succulent structures called lodicules,
which are adnate to the palea. At the
time of flowering, the lodicules help
push apart the lemma and palea at
the base to expose the stamens and
the pistil.
—The androecium (male reproductive
organ, Fig. 2.5) has six stamens
in two whorls. Anthers are
Rice plant and its environment 7