Xylem is a complex tissue that performs the vital function of transporting water and dissolved minerals from the roots to the aerial parts of the plants, such as stems, leaves, and flowers. It is one of the two important transport tissues found in plants, the other being phloem. The secondary walls of the xylem cells consist of lignified cell walls that provide structural support to the plant. The hollow interior of the xylem cells facilitates the movement of water and minerals in the upward direction, which is commonly referred to as ascent of sap.
The xylem tissue is primarily composed of two cell types, vessel elements and tracheids. The vessel elements are short and wide cells that are found in the angiosperms, while tracheids are narrow and elongated cells commonly found in both angiosperms and gymnosperms. The cell walls of these cells are impregnated with lignin, which provides mechanical support to the plant.
The movement of water and minerals in the xylem tissue is facilitated by transpiration pull, which is generated by the loss of water vapor through the leaves. The cohesive and adhesive properties of water molecules also play an important role in transporting water in the xylem tissue. The cohesive property of water molecules allows them to bind together, while the adhesive property allows them to adhere to the hydrophilic walls of the xylem cells.
The xylem tissue also plays an important role in maintaining the turgor pressure and rigidity of the plant. The uptake of water and minerals from the soil by the roots generates a positive pressure gradient in the xylem tissue, which in turn maintains the turgor pressure and prevents wilting of the plant.
In conclusion, the xylem tissue is an important component of plant physiology, which plays a crucial role in the transport of water and minerals and maintaining the structural integrity of the plant. Understanding the xylem system is essential for understanding plant growth and developing novel strategies for improving crop productivity.