Grass leaf. Light micrograph of a section through a leaf of the grass Psamma arenaria (Graminae). At upper centre is a vascular bundle, oval-shaped, surrounded by a sheath of sclerenchyma one cell thick. The vascular bundle contains vessels of xylem (large empty cells) which conduct water; and phloem (red) which conducts nutrients through the plant. The external cortical cells of the leaf have an elaborate arrangement. Leaf hairs on the surface of the epidermis, seen here, are in some grasses hardened into small scales of silica that protect the leaf from attack. Magnification: unknown.