Fig. 25.—Transverse section of the stem of Pennisetum cenchroides. × 20
The epidermal cells are all thickened very much and the outer layer is cutinized and impregnated with silica. This is the case in the epidermis of the stems and leaves of most grasses. (See fig. 24.)
In order to give a general idea of the variations in the structure of the stem in grasses a few examples are chosen and the details of the structure of the stems of these grasses are dealt with here.
Fig. 26.—Transverse section of a portion of the stem of Pennisetum cenchroides. × 70
1. Epidermis; 2. sclerenchyma; 3. vascular bundle.
The stem of Pennisetum cenchroides is somewhat round in outline in the transverse section with a slight curvature in the front. The vascular bundles are rather numerous and irregularly scattered all over the ground tissue. The peripheral bundles are not so close to the periphery of the stem as in Rottboellia exaltata. These are separated from the epidermis by several layers of parenchymatous cells. Further, these peripheral bundles are all imbedded in a continuous sclerenchymatous band which runs round the stem in the form of a ring. The epidermal cells as well as the layer of cells in immediate contact with it are thick-walled. In the vascular bundles of the ground tissue the bundle-sheath is rather prominent and the phloëm portion is well developed. (See figs. 25 and 26.)