empty but the others bearing flowers in
their axils. The glumes are two-ranked and imbricating. As a type for
the spikelet that of an Eragrostis or Dinebra may be chosen. (See fig.
17.) In this spikelet the rachilla bears a number of glumes alternating
and imbricating. The first two glumes at the base of the spikelet do not
bear any flowers and so these two glumes are usually called empty
glumes. This is the case in almost all the species of grasses. The third
and the subsequent glumes are regularly arranged on the slender rachilla
alternately in two rows. In the axils of each of these glumes there is a
flower, except perhaps in the topmost glume. The flower is usually
enclosed by the glume and another structure found opposite the glume and
differing very much from the glume. This is the =palea=. It is attached
to the axis of the flower and its back is towards the rachilla.
Generally there are two nerves in a palea and its margins are enclosed
within those of the glume. The palea is homologous with the prophyllum
which it very much resembles. The prophyllum is usually found in the
branches of grasses, but it is not confined to grasses alone. It occurs
in the branches of some species of Commelina.

The spikelets vary very much in their structure. The spikelets in
grasses of several genera consist of only four glumes. As usual the
first two glumes are empty and the remaining two are flower-bearing
glumes. Both these glumes may have perfect flowers as in Isachne or the
terminal one may contain a perfect flower, the lower having either a
staminate flower or only a palea. Very often the spikelets are unisexual
and the male and female spikelets may be on the same plant as in _Coix
Lachryma-Jobi_ and _Polytoca barbata_, or they may be on different
plants as in _Spinifex squarrosus_.

The glumes of a spikelet are really modified bracts and some
differentiate the flowering glumes from the empty ones, by giving them
different names. The first two empty glumes are called glumes by all
agrostologists. Some in Europe call the flowering glume lower palea to
distinguish it from the real palea which they call the upper palea. Some
American Authors have recently adopted for the flowering glume the term
=lemma= introduced by Piper.

Considerable variation is met with in the case of the empty glumes.
Generally they are unequal, the first being smaller. Very often the
first glume becomes very small and it may be altogether absent. In som