Phloem is mostly living tissue, responsible for transporting sugars and other nutrients throughout a plant. However, it also contains some dead cells.
Phloem is a complex tissue composed of several cell types, which include:
- Sieve Tube Elements: These are the main conducting cells of the phloem. They are living cells but lack a nucleus at maturity. They are connected end-to-end, forming long sieve tubes.
- Companion Cells: These are closely associated with sieve tube elements. They are living cells and provide metabolic support to the sieve tube elements, which lack nuclei.
- Phloem Parenchyma: These are living cells that store and release food substances and perform other metabolic functions.
- Phloem Fibers: These are sclerenchyma cells, which are typically dead at maturity. They provide structural support to the phloem tissue. These fibers, also known as bast fibers, have thick walls and a narrow lumen.
Therefore, while the sieve tube elements, companion cells, and phloem parenchyma are living, the phloem fibers are dead. The phloem, as a whole, functions because of the coordinated activity of both living and dead cells.
