Final answer:
Structure x on each root is the stele, which is central to the root's vascular system and is surrounded by the endodermis.
Step-by-step explanation:
The structure x on each root likely refers to the stele, which is the central part of the root containing vascular tissue. This vascular tissue consists of xylem and phloem, which transport water, minerals, and nutrients. The stele is enveloped by a crucial layer called the endodermis, which serves as a selective barrier with its Casparian strip made of a waxy substance called suberin that ensures proper material passage into the vascular system of the root.
In the case of dicot roots, the vascular tissue within the stele is arranged in an 'X' shape, while in monocot roots, it is arranged as a ring around the central pith. The outermost layer of the root's vascular tissue is the pericycle, which can produce lateral roots. Root structures can also undergo modifications to serve different functions, such as storage of starch or additional support in the form of aerial roots.
The name of structure x is the stele, central vascular tissue in roots.