What xylem is and where it is

What xylem is and where it isXylem is a plant vascular tissue. It is in the innermost part of stems, leaves and roots of vascular plants. Its functions are to transport water and mineral salts dissolved from the roots to the aerial parts of the plant, support, maintain the water balance of the plant, and contains reserve material.

Water is a vital element for plants, both for their role in photosynthesis, and also because they are the means to dissolve minerals. This water is taken from the roots to be carried up with the help of perspiration, but this happens thanks to an inner tissue called xylem.

Along with phloem is part of the vascular system of the plants. In this article we will explain in detail what xylem is, where it is and its functions.

What xylem is and where it is

Xylem is a plant vascular tissue, also known as woody tissue. It is located in the vascular or tracheofite plants, and within them is distributed throughout the organs of the plant, that is, by roots, stem and leaves. It is arranged near the central marrow, in the innermost part of the plant. They settle down thanks to vascular beams.

It is composed of tracheal elements or xylema vessels, which are lifeless cells. They are born with a functional and alive nucleus, but evolved to die later and manage to eliminate the entire cytoplasm, leaving the cell empty to function as simple channels. Another important characteristic of the tracheal elements is that the walls are thick due to the presence of lignina.

Under these tracheal elements we have two types:

  • Tracheas or elements of the glasses: they come together to form long connected, tube-shaped vessels. It has holes in the cross-section wall, i.e. at the terminal ends, with which they intercommunicate with the next cell. They are found in angiosperms, which are plants with flower and fruit, in the Gnetales belonging gymnospermas, and a few ferns, because they are more modern, in the sense that they are more efficient for the passage of water from one cell to another.
  • Tracings: they have irregular spindle shape with the elongated ends, and overlap some being narrower and shorter than the tracheas. They are found only in the gymnosperms, a group containing the ferns and conifers. They have many dotted on the side walls with which the canals communicate, but lack the transverse holes. They’re more primitive.

In addition, other non-vascular elements are accompanied by xylem, which are:

  • woody or sclerenquito fibers
  • Parenchymatic cells

There are two types of xylem:

  • Primary Xylem: originates from the procambium. It has two types of xylem: protoxylem and metaxylem. The first occurs when the plant is barely growing in length and when it is developing each organ, while the metaxylem exists when the plant is generated when the plant no longer lengths, but is still young.
  • Secondary Xylem: originates from the cambium and occurs when the plant is increasing throughout. Every year new rows of this secondary xylem form, and this is what we observe as rings in tree trunk cuts. In spring these rings are thicker, and in autumn thinner.

Functions of plant xylem

The main function of xylem is to transport water and minerals from the roots by the stem to the leaves of the plant, that is, its direction is always upward. Such components it carries are known as raw sap or cell sap. This function comes from the trachea and tracheids.

The sap can defy gravity and run upwards, even in trees several meters high. This is the case thanks to the theory of cohesion-tension. What happens is that the leaves sweat water into the atmosphere, creating a pull of the water inside the plant because of the great cohesion between its molecules that pulls upwards. Therefore, xylem plays an important role in the water balance of the plant.

Another important function is that of support, provided by the strong walls of lignin, and by the woody fibers that give rigidity to the plant. It also serves as a reservoir of nutrients, coming from parenchymatic cells. These provide hormones, amino acids, mineral salts, among others.

Difference between xylem and phloem

Xylem and phloem together form the plant vascular tissue and, therefore, the vascular system. Each has particular functions and morphology. We can find the following differences between the two:

  • Function: xylem transports water and mineral salts, while the phloem transports especially nutrients, and also a little water. Xylem is the main conveyor tissue of the vital liquid.
  • Location: the xylem is located further inside the plant, and the phloem is more external. Looking at a trunk cut, the growth rings are made up of several layers of xylem, while the phloem is only found in a layer under the crust.
  • Transportation direction: xylem is necessarily one-way with movement from the bottom up, but the phloem is two-way.
  • Type of cells: xylem cells have no life, but those in phloem are alive.
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