utgrowths of the epidermis. The roughness of the surface of
the leaves of grasses is due to the presence of very minute short hairs
borne by the epidermis. In most cases these short hairs are found in
regular rows. Although the epidermis is more or less even in the leaves
of several grasses such as _Panicum repens_, _P. flavidum_ and
_Eriochloa polystachya_, it is wavy or undulating in the leaves of a few
grasses. For example, the upper epidermis in the leaves of _Panicum
fluitans_ is undulating as it follows the contour of the ridges and
furrows.

The epidermal cells have even surfaces in the leaves of most grasses but
in some they bulge out. In the leaves of _Panicum flavidum_ the cells of
the lower epidermis are quite even, whilst those of the upper epidermis
bulge out. The cells of both the upper and the lower epidermis are
distinctly bulging out in the leaves of _Panicum colonum_. In _Panicum
fluitans_ the cells of the upper epidermis bulge out so much as to form
distinct papillae.

The free surface of the epidermis is more or less cutinised in the
leaves of all grasses. In some leaves the cuticle is very thick and even
papillate as in the leaves of _Aristida setacea_ and _Panicum repens_
whilst in others it is very thin, as in the leaves of _Panicum colonum_
and _P. fluitans_. Cutinisation is rather prominent in the leaves of
grasses growing under dry conditions and it is less pronounced in
mesophytic grasses.

[Illustration: Fig. 64.--Transverse section of a portion of the leaf of
Panicum colonum. x 120

1. Motor cells; 2. stomata; 3. sclerenchyma; 4. chlorophyllous layer.]

[Illustration: Fig. 65.--Transverse section of a portion of the leaf of
Panicum fluitans. x 120

1. Motor cells; 2. stomata; 3. sclerenchyma; 4. chlorophyllous layer.]

As regards size, the epidermal cells overlying the sclerenchyma are
small and those lying over parenchyma are larger. Amongst the larger
cells some may be motor-cells. The stomata occur in regular rows between
the vascular bundles and they are quite characteristic of grasses. They
are more or less similar in structure in all grasses. In the leaves of
many grasses stomata are found in both the upper and the lower epidermis
and they are confined to the lower epidermis in a few grasses only.

The motor-cells vary very much both as regards their shape and position.
In some leaves as in the leaves of the grass _Panicum flavidum_ the
motor-cells are confined to the midrib o