Xylem
- The xylem is a complex tissue responsible for conducting water and minerals from the roots to the rest of the plant.
- It is composed of several types of cells, including vessel elements, tracheids, fibers, and parenchyma cells.
- These cells are all alive when they are functioning, as they are responsible for the transport of water and minerals.
- Therefore, xylem tissue is not composed mainly of dead cells.

Phloem
- The phloem is another complex tissue responsible for conducting food materials, such as sugars, from the leaves to the rest of the plant.
- It consists of sieve tube elements, companion cells, fibers, and parenchyma cells.
- These cells are also alive when they are functioning, as they are responsible for the transport of food materials.
- Therefore, phloem tissue is not composed mainly of dead cells.

Epidermis
- The epidermis is the outermost layer of cells in plants.
- It is a protective layer that covers the plant's surfaces, such as leaves, stems, and roots.
- The cells of the epidermis are alive and actively contribute to the plant's functions, such as gas exchange and protection against pathogens.
- Therefore, epidermis tissue is not composed mainly of dead cells.

Endodermis
- The endodermis is a single layer of cells that surrounds the vascular tissue in roots and stems.
- It acts as a selective barrier, controlling the movement of water and minerals into the vascular tissue.
- The cells of the endodermis are alive and have specialized structures, such as Casparian strips, which regulate the flow of substances.
- Therefore, endodermis tissue is not composed mainly of dead cells.

Conclusion
- Among the given options, the tissue that is composed mainly of dead cells is the epidermis.
- The epidermis consists of dead cells that form a protective layer on the surface of the plant.
- These cells are often filled with a substance called suberin, which provides additional protection against water loss and pathogens.
- The dead cells of the epidermis are continuously replaced by new cells produced in the underlying meristem tissue.