The vascular system in a plant plays an important role in the life of these herbal being. It conducts water, nutrients, sugars, proteins and RNA through the plant through lignified tissues. Vascular tissue allows the plants to grow larger than non-vascular plants.
The xylem and phloem are the parts of the plants vascular system which conducts the elements. These are usually located together in vascular bundles but their positions to each other can vary. When the xylem and phloem lie together, but the xylem is to the outside it Is called a collateral arrangement. When the xylem is between two phloem it is a bicollateral arrangement. If xylem is surrounded by phloem it is called an amphicribral arrangement.
These two parts of the vascular system are formed when the plant begins to grow from the apical meristem which is at the top of the shoot. At this time undifferentiated cells become differentiated into procambium. This then differentiates into xylem and phloem.
The vascular tissue needs to develop in the correct location, in columns so that they xylem and phloem cells line up. This assists their performance as they perform like pipes In a house.
In the vascular tissue, xylem is responsible for transporting water and nutrients from the roots to the parts of the plant which are above ground. They also transport hormones and other small molecules.
When photosynthesis occurs in a plant they need a system to help carry the food where it is needed. The phloem is responsible for transporting sugars from their source, like leaf cells, to sink tissues, like root cells or flowers. Phloem tissue is always alive, unlike xylem tissues which dies after one year. When sap drips from a tree, this sap usually comes from the phloem tissue. Phloem cells are usually located along the underside of leaves. This is why aphids can be found along this part of the leaf, they are looking for the sugar that the phloem is transporting.
Between the xylem and phloem is the vascular cambium. This is the area that separates the xylem and phloem from each other. This is also where stem cells are located which will eventually differentiate into both of these. Sunlight and nutrients ae the determinates of the rate of growth of the cells from the vascular cambium. This growth pattern can be witnessed in the rings found in a tree trunk. As long as the vascular cambium produces new cells, the plant will become more stout. This growth rupture the epidermis of the stem, so cork cambium is also found in woody plants. These cells become cork cells which protect the surface of the plant. They also reduce the amount of water than may be loss.