Fig. 45.—Transverse section of the entire root of Andropogon Sorghum. × 25
Fig. 46.—Transverse section of the cortical portion of the root of Andropogon Sorghum. × 150
r.h. Root-hair; p.l. piliferous layer; ex. exodermis; co. cortex.
The rest of the root forming the central core is the stele and at its periphery there is a single layer of cells called the pericycle. The arrangement of the xylem and the phloëm is different from that of the stem. They lie side by side on different radii, and not one behind the other on the same radius as in the stem. The number of xylem groups is fairly large and the development of the xylem is from the pericycle towards the centre of the stele. (See figs. 44 and 45.) The parenchymatous cells in the centre of the stele become thick-walled in older roots.
Structure of the leaf.—The structure of the leaf of grasses is quite characteristic of the family. In every leaf a number of vascular bundles, some small and others large, pass from the base to the apex. Externally the leaf is covered on both the sides by the epidermis. The spaces existing between the vascular bundles and the epidermis are filled with parenchymatous cells. The larger vascular bundles consist of xylem and phloëm surrounded by a bundle sheath of a single layer of cells. In the smaller bundles the xylem is very much reduced. Around every vascular bundle there is a single row of somewhat large cells densely packed with large chloroplasts, the chlorophyllous layer. The vascular bundles are strengthened by fibres, on both the sides in the case of larger bundles and on only one side in small bundles.
