by sclerenchyma on the lower side and others have none. The
spaces between the bundles are occupied by thin-walled parenchymatous
cells containing small chlorophyll grains.

[Illustration: Fig. 49.--Upper epidermis of the leaf of Panicum
javanicum. x 300]

[Illustration: Fig. 50.--Lower epidermis of the leaf of Panicum
javanicum. x 300]

The lower epidermis of the leaf in the transverse section is even and
consists of small and large round cells. The upper epidermis is slightly
wavy and it is made up of some small round cells alternating with groups
of larger cells. The epidermal cells lying over sclerenchyma and the
smaller vascular bundles are small and round, while those lying over the
furrows between the vascular bundles are large and are called =motor= or
=bulliform cells=. The presence of motor cells is a characteristic
feature of the leaves of many grasses.

The continuity of both the upper and the lower epidermis is interrupted
by the stomata. Air-cavities are seen below these stomata. The
arrangement of the stomata, the shape of the guard cells and the
characteristics of the epidermal cells become clear on examining a piece
of epidermis. (See figs. 49 and 50.)

The structure of the leaf of _Panicum javanicum_ may be taken as typical
of the structure of the leaves of most grasses. The leaves of _Eriochloa
polystachya_, Cynodon and Paspalums are very much like the leaves of
_Panicum javanicum_ in their internal structure.

Considerable amount of variation, however, occurs in the leaves of
grasses especially as regards the arrangement of fibres and motor cells.

[Illustration: Fig. 51.--A portion of the transverse section of the leaf
of Eriochloa polystachya x 120

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

Every large primary vascular bundle in the leaves of many grasses
possesses sclerenchymatous bands both above and below. The other
vascular bundles may have bands of sclerenchyma on both sides or on one
side only or none. For example, in the leaves of _Panicum repens_ both
the primary and secondary bundles are provided with sclerenchyma on both
the sides, while those of the third order may have it on one side or
not. The hyaline margin of this leaf and of the leaves of other grasses
consists entirely of sclerenchyma. (See fig. 53.)

[Illustration: Fig. 52.--Transverse section of a portion of the leaf of
Panicum repens. x 120

1. Motor cells; 2. stomata; 3. sclerenchyma;