Xylem vessels

Perforated and pitted secondary walls of dead vessel member cells form these water-conducting tubes, which vary in size and in shape.
B The thick secondary walls of dead xylem cells connect to make long, water-con-ducting tubes. Lignin deposited in rings or spirals strengthens the walls. Perforation plates impart strength to a junction where vessel members meet, while also allow-ing water to flow through the tube. The micrograph shows a perforation plate in a section of magnolia (Magnolia grandifolia). Pitted walls of tracheids are also visible.