Phloem. Light micrograph of phloem tissue from a plant stem. The phloem is living tissue that transports carbohydrates and plant hormones around the plant body. It consists of sieve tubes, through which the material moves, and companion cells. The sieve cells have sieve plates (vertical lines with red blobs), a cell wall with holes to allow the passage of solutes. The companion cells, which are between sieve cells, carry out protein synthesis and other metabolic functions for the sieve cells.