The phloem is the vascular tissue that carries out the function of translocation (i.e. the process of transporting photosynthate materials from the photosynthetic plant organs to various parts of the plant). The phloem is comprised of the following major components: (1) sieve elements, (2) companion cells, (3) phloem sclerenchyma, and (4) phloem parenchyma.
The phloem sclerenchyma includes the phloem fibers and the sclereids. Both the phloem fibers and the sclereids are dead cells at maturity. They lose their protoplast and form secondary wall thickenings in between the primary cell wall and the plasma membrane. The secondary cell wall is thickened with lignin. Thus, they are efficient at providing mechanical support. The phloem fibers though do not limit flexibility as the sclereids do.
The phloem fiber is narrow and elongated. It occurs both in the primary phloem and the secondary phloem. However, it is not often present in the metaphloem. In secondary phloem, the phloem fibers form the bast fibers, which some of them are commercially important.
- phloem fibre (British)