Phloem tissue is made up of several different cell types including sieve tube elements and companion cells, cells that are active in the transport of sugars and other organic compounds.

Unlike the specialized cells of the xylem, these cells are alive maturity. Transport of sugars occurs through the sieve tube elements which connect up end to end to form sieve tubes. Sieve plates form at the end walls of each sieve tube element, and the protoplast of adjacent cells are joined through holes in the sieve plates. Companion cells are connected to sieve tube elements and appear to be important in moving sugars in and out of the adjacent sieve tube element. In addition to these two specialized cell types both fibers and parenchyma cell types occur in phloem tissue.