The upper and the lower surfaces of the leaves of many grasses are more or less even, but in the case of a few grasses the upper surface consists of ridges and furrows, instead of being even. In the leaves of _Panicum repens_ and _Eragrostis Willdenoviana_ the upper surface is wavy and consists of shallow furrows and slightly raised ridges. But in the leaves of _Aristida setacea_ and _Panicum fluitans_ the furrows are deeper and the ridges are more prominent. In _Aristida setacea_ the ridges are flat-topped and they are rounded with broad furrows in _Panicum fluitans_. [Illustration: Fig. 62.--Upper epidermis of the leaf Panicum Isachne. x 200 1. Cells overlying the veins; 2. cells overlying the furrows; 3. stomata.] [Illustration: Fig. 63.--Lower epidermis of the leaf Panicum Isachne. x 200 1. Cells overlying the veins; 2. cells overlying the furrows; 3. stomata.] The epidermis covering the leaves consists of elongated cells with plane or sinuous walls, various kinds of short cells intercalated between the ends of long cells, motor-cells and stomata. Hairs of different sorts occur as outgrowths 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.]