Root cross sections: The outer layer of a eudicot root is called the epidermis. To the inside of the epidermis is the ground tissue, called the cortex. In most eudicots, the vascular tissue forms a solid vascular cylinder in the center of the root. The vascular cylinder consists of a lobed core of xylem, with phloem between the lobes of xylem. The innermost layer of ground tissue, known as the endodermis, regulates passage of substances into the vascular cylinder. The outer layer of a monocot root is called the epidermis. As in eudicots, to the inside of the epidermis is the ground tissue, called the cortex. However, the structure of the vascular cylinder in many monocot species differs from most eudicots. At the center is a core of parenchyma cells, surrounded by alternating rings of xylem and phloem. As in eudicots, the innermost layer of ground tissue, known as the endodermis, regulates passage of substances into the vascular tissue.
