Fig. 5.1-1. Transverse section of a grass leaf (Poa). This is a transverse section through a vascular bundle and a mass of sclerenchyma cells fibers, in this case that runs the length of the leaf. Although the sclerenchyma cells appear spherical here, in longitudinal section, they would be very long. These cells have both primary and secondary walls that contain lignin, so the dye Safranin has stained them red. The cells on the sides of the micrograph are parenchyma cells with unlignified primary walls, so despite being exposed to Safranin, they have stained green due to the presence of Fast Green in the Safranin/Fast Green staining procedure. The epidermis cells too have stained red, almost certainly because they have cutin in their walls, rather than lignin (Safranin is not a specific stain that reacts with only one chemical). The large cells in the vascular bundle are vessel elements, xylem cells that conduct water; they are a type of conducting sclerenchyma.