Phloem is the tissue system responsible for the movement of food materials in the plant - especially sugar made through photosynthesis.
Phloem is made up of several cell types:
- Sieve elements
- Companions cells
- Ray parenchyma cells
- Phloem fibers
The sieve tube member is a mature phloem cell involved with long distance movement of food material.
They are living cells, but lack a nucleus. The protoplasts are connected through sieve areas between cells that conduct materials.
Companion cells are parenchyma cells that function to load and unload material into the sieve tube member.
The sieve plate is a perforated area at the top of the sieve tube member.
The sieve plate is formed between two cells as a portion of the connecting cell wall is degraded.
Companion cells are parenchyma cells that function to load and unload material into the sieve tube member. Companion cells have a nucleus, while sieve tube members do not.
This sieve tube member seen in longitudinal section shows the sieve area.
There are numerous sieve areas on the sides of the sieve tube that connect one sieve tube with another.
Sieve tube members are formed from phloem initials in conjunction with the companion cells.
Phloem initial with a large vacuole and a nucleus.
A companion cell forms associated with the sieve tube.
The companion cell divides to form two or more cells. The perforations in the sieve plate begin to form. The nucleus begins to dissolve.
Sieve plate is well formed. The nucleus is gone and the vacuole membrane begins to dissolve.
The vacuole dissolves further.
A mature sieve tube element with the pores open on the sieve plate.
The stages of phloem element formation.
Ray Parenchyma is a group of living cells formed in the vascular cambium and extending into the secondary xylem and phloem.
A ray's principle function is as storage tissue in a woody stem.
Ray in cross-section of a linden stem.
There are also fibers in the phloem tissue.
These fibers are important for structural support.