Xylem & Phloem
Xylem: -Transports water and soluble materials.
Phloem: -Transports sugars.
- The vascular bundle is found in the centre.
- The arrangement provides strength to withstand the pulling forces to which roots are exposed/
- Around the vascular bundle the cells are called the endodermis - they help to get water into the xylem vessels.
- Inside the endodermis is the pericycle: contains meristem cells that can divide.
- The vascular bundles found near the outer edge of the stem.
- Xylem is found towards the inside of each vascular bundle; phloem is found towards the side.
- In between the xylem and phloem is a layer of cambium.
- Cambium is a layer of meristem cells that divide to make new xylem and phloem.
- A dicotyledon leaf has a branching network of veins that get smaller as they branch away from the midrib.
Structure of Xylem
- Consists of tubes for water, fibres for support and living parenchyma.
-Long cells with thick walls containing lignin.
-Lignin waterproofs walls of cells and strengthens them.
-Cells die and end decay, forming a long tube
-Lignin forms spiral, rings or broken rings.
-Some lignification is not complete, and pores are left called pits, allowing water to move between vessels.