The four phloem cells

Phloem is the other complex tissue, and it is built the same way — four kinds of cell — but the living-and-dead balance is almost exactly the reverse of xylem’s.

Figure to be added

Figures 1.12 and 1.13 — phloem tissue in two views. The longitudinal section shows a sieve tube made of sieve tube elements stacked end to end, with a perforated sieve plate at each join, a narrow companion cell running alongside, and phloem parenchyma beside that. The cross-section shows the same cells cut across: a large sieve tube cell with its sieve plate, a small dense companion cell tucked against it, and parenchyma cells around them.

Cell type	Living or dead	What it does
Sieve tube cells (sieve tube elements)	Living	Joined end to end into sieve tubes that carry food
Companion cells	Living	Elongated cells beside the sieve tubes; their nucleus controls the sieve tube cell
Phloem parenchyma	Living	Thin-walled cells lying among the rest
Phloem fibres	Dead	Scattered here and there through the tissue; provide strength

Three living and one dead — the mirror image of xylem

In xylem, three cell types are dead and one is alive. In phloem, three are alive and one is dead. That difference follows from what each tissue carries: water can be pushed and pulled through empty tubes, but moving food takes energy, and only a living cell can spend it.

The function of phloem

Transporting the food produced in the leaves throughout the plant body. This is called translocation.