Fluorescence light micrograph section through the stem of a maize, or corn (Zea mays), plant. The stem is the part of the plant that supports the leaves and transports water, nutrients, and sugars between the roots and the rest of the plant. A section through the stem of Zea mays shows a distinct pattern of tissues, arranged in concentric rings. Starting from the outermost layer, the stem is covered by a layer of protective tissue called the epidermis, which is made up of a single layer of cells. Below the epidermis is the cortex, which consists of several layers of parenchyma cells that provide structural support to the stem. The next layer is the endodermis, which is a single layer of cells that separates the cortex from the inner tissues of the stem. The endodermis plays a key role in regulating the movement of water and nutrients into the central cylinder of the stem. Inside the endodermis is the stele, which is the central cylinder of the stem that contains the vascular tissues responsible for transporting water, nutrients, and sugars throughout the plant. The stele is composed of two main tissues: the xylem and the phloem. The xylem tissue is responsible for transporting water and minerals from the roots up to the leaves, while the phloem tissue transports sugars from the leaves to the rest of the plant. The xylem tissue in Zea mays is located towards the centre of the stem and is made up of two types of cells: tracheids and vessels. The phloem tissue is located towards the outside of the stem and is made up of two types of cells: sieve tubes and companion cells.