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 on the upper surface. The epidermal cells of this leaf are large and uniformly round. (See figs. 66 and 67.) [Illustration: Fig. 66.--Transverse section of a leaf of Panicum flavidum. x 20 1. Vascular bundle; 2. sclerenchyma; 3. motor-cells.] [Illustration: Fig. 67.--Transverse section of the leaf of Panicum flavidum. x 150 1. Motor-cells; 2. stomata; 3. sclerenchyma; 4. chlorophyllous layer.] In the case of most grasses the motor-cells are found in groups of three, four or five between the vascular bundles. The central motor-cell is usually the largest and it is somewhat obovate in shape in a transverse section of the leaf. In the leaves of _Panicum javanicum_ and _Eriochloa polystachya_ there are three or four motor cells in the group and the group consists of four, five or rarely six motor cells in the leaves of _Eragrostis Willdenoviana_. When there are distinct furrows between ridges these cells lie in the furrows and they are many in number. In the leaves of _Panicum repens_ there are five to seven motor-cells in the furrows and the single row of cells stretched between the motor-cells and the lower epidermis in the furrow consists of more or less clear cells with sparsely scattered small chlorophyll grains. (See fig. 52.) The motor-cells occupying the furrows in the leaves of _Aristida setacea_ are more in number than in _Panicum repens_ and are of a different shape. All the cells lying in the furrow between the motor-cells and the sclerenchyma are clear cells free from chlorophyll grains. Although the motor-cells differ in shape from the ordinary epidermal cells in most grasses, there are, however, a few grasses in which the motor-cells do not differ very much from the epidermal cells except in size. For example, in the leaves of _Panicum colonum_ the motor-cells are just like the ordinary epidermal cells in shape but are larger. (See fig. 64.) Motor-cells are usually confined to the upper epidermis, but they may also be found in the lower epidermis. In the leaves of _Pennisetum cenchroides_ motor-cells are found in both the upper and the lower epidermis, the group in the upper epidermis alternating with that in the lower. [Illustration: Fig. 68.--Transverse section of a portion of the leaf of Pennisetum cenchroides. x 100