Xylem and phloem are both transport vessels that combine to form a vascular bundle in higher order plants
- The vascular bundle functions to connect tissues in the roots, stem and leaves as well as providing structural support
Xylem
- Moves materials via the process of transpiration
- Transports water and minerals from the roots to aerial parts of the plant (unidirectional transport)
- Xylem occupy the inner portion or centre of the vascular bundle and is composed of vessel elements and tracheids
- Vessel wall consists of fused cells that create a continuous tube for the unimpeded flow of materials
- Vessels are composed of dead tissue at maturity, such that vessels are hollow with no cell contents
Phloem
- Moves materials via the process of active translocation
- Transports food and nutrients to storage organs and growing parts of the plant (bidirectional transport)
- Phloem occupy the outer portion of the vascular bundle and are composed of sieve tube elements and companion cells
- Vessel wall consists of cells that are connected at their transverse ends to form porous sieve plates (function as cross walls)
- Vessels are composed of living tissue, however sieve tube elements lack nuclei and have few organelles
Comparison of Xylem and Phloem
