xylem

• Xylem vessels are very long, tube-like structures formed from cells joined end to end. There are no end walls on these cells, making an uninterrupted tube that allows water to pass up through the middle easily. The cells are dead, so they contain no cytoplasm.
• • The cell walls are thickened with a woody substance called lignin, which helps to support the walls and stops them collapsing inwards.
  • Lignin can be deposited in xylem walls in different ways, e.g. in a spiral or as distinct rings.
  • Being deposited in these patterns allows flexibility and prevents the stem from breaking.
  • The amount of lignin increases as the cell gets older.
• Water and mineral ions move into and out of the vessels through small pits in the walls where there's no lignin. This is how other types of cells are supplied with water.
• xylem vessel

  A) no end walls between cells

  B) pit

  C) water