The cells that conduct water in plants are tracheids or vessel members, both of which make up the plant tissue known as xylem. The type of cell predominant in xylem depends on the type of plant, but most species in all groups have at least some tracheids.
Tracheids are the only types of cells that conduct water in seedless vascular plants, such as ferns, and most gymnosperms, such as pine trees. Tracheids are narrow and elongated hollow cells. They have thin, modified cell walls known as pit membranes. The membranes permit passage of water between vessels while protecting against damaging air bubbles.
Vessel members are very similar in basic shape to tracheids, but they are even more specialized to carry water efficiently. Instead of pit membranes, they have perforations, which are areas that lack both a cell wall and a cell membrane. These allow water to pass very easily between cells, but they provide less protection against air bubbles. As a result, the cells are more likely to suffer fractures and disruptions. Vessel members are the primary cells in the xylem of flowering plants.
Both types of cells are accompanied by fiber cells that provide structural support. In woody plants, the cells that make up xylem tissue form rings, with only the outermost ring living, and the rest provide support for the plant.