Substances transported by different vessels in plants:

Xylem:
- Water: Xylem vessels transport water and dissolved minerals from the roots to the leaves of the plant.
- Minerals: Inorganic nutrients like nitrogen, phosphorus, and potassium are also transported through xylem vessels.
- Support: Xylem vessels provide structural support to the plant, helping it maintain an upright position.

Phloem:
- Sugars: Phloem vessels transport sugars produced during photosynthesis from the leaves to other parts of the plant, such as roots, flowers, and fruits.
- Hormones: Plant hormones like auxins, cytokinins, and gibberellins are also transported through phloem vessels, regulating growth and development.
- Signaling molecules: Phloem sap contains signaling molecules that help coordinate various physiological processes in the plant.

Comparison:
- Xylem primarily transports water and minerals, while phloem transports sugars and signaling molecules.
- Xylem vessels are made up of dead cells with lignin, providing structural support, whereas phloem vessels are made up of living cells called sieve tubes.
- Xylem transport is unidirectional, from roots to shoots, while phloem transport can be bidirectional, depending on the plant's needs.