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Xylem is one of the two types of transport tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts of the plants such as stems and leaves, but it also transports nutrients .
Because phloem tubes are located outside the xylem in most plants, a tree or other plant can be killed by stripping away the bark in a ring on the trunk or stem. With the phloem destroyed, nutrients cannot reach the roots, and the tree/plant will die.
Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem Detail of the vasculature of a bramble leaf Translocation in vascular plants. Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem ...
Xylem is the water-conducting tissue, and the secondary xylem provides the raw material for the forest products industry. [25] Xylem and phloem tissues each play a part in the conduction processes within plants. Sugars are conveyed throughout the plant in the phloem; water and other nutrients pass through the xylem.
There is also a tissue between xylem and phloem, which is the cambium. The xylem typically lies towards the axis ( adaxial ) with phloem positioned away from the axis ( abaxial ). In a stem or root this means that the xylem is closer to the centre of the stem or root while the phloem is closer to the exterior.
The phloem tissue arises from the cell facing outside and consists of sieve tubes and their companion cells. The function of phloem tissue is to distribute food from photosynthetic tissue to other tissues. The two tissues are separated by cambium, a tissue that divides to form xylem or phloem cells.
With much of the sucrose having been removed, the water exits the phloem by osmosis or is drawn by transpiration into nearby xylem vessels, lowering the turgor pressure within the phloem. [4] The sucrose concentration in sieve tubes is typically 10–30% in the leaves but only 0.5% in the photosynthesis cells.
The fascicular and interfascicular cambia thus join up to form a ring (in three dimensions, a tube) which separates the primary xylem and primary phloem, the cambium ring. The vascular cambium produces secondary xylem on the inside of the ring, and secondary phloem on the outside, pushing the primary xylem and phloem apart.